Hyposalinity

[CoralB]

Nice thread !!!

Hyposalinity
Jay Hemdal 2021

This term refers to a long-term bath treatment for marine fishes in which the salt content of the water is lowered and held below the point that certain parasites can survive. The salt level reached, and the time of the treatment are the two variables. Hyposalinity can be used as a primary treatment against certain marine fish diseases (see below) or as a component of an active quarantine for newly acquired fish.

To clarify for beginners: you cannot perform hyposalinity on fish when invertebrates are in the tank. You must isolate the fish to a fish-only situation.

Before instituting a hyposalinity treatment, you need to decide what measurement units you plan on using – salinity or specific gravity. Then, you must have a very accurate measuring device. A laboratory grade hydrometer is best for accurate specific gravity measurements, or to standardize another measurement means. The device employed must be capable of accurately measuring down to one part per thousand, or one specific gravity unit. Better yet is a device that can read to twice that resolution. For example; capable of measuring 16.5 ppt or 1.0125 specific gravity units. Most handheld refractometers are not accurate enough. Swing arm hydrometers can measure this small of a difference, but they must be first checked for accuracy against a laboratory hydrometer.

There are two basic means to administer a hyposalinity treatment: in the display tank or in a quarantine/treatment tank. Invertebrates and some algae cannot survive hyposalinity, so must be removed prior to a hyposalinity treatment (of course, they then need to be cleared of potential disease by use of a proper fallow period). There are benefits and drawbacks to administering hyposalinity in these two modes:

Quarantine tank: Little to no microbiome die-off. Less salt lost. Ability to add other medications during the process if required. System may not be biologically robust enough to manage ammonia levels. Poor pH buffering. Requires a second aquarium and letting the infected display tank go fallow. Ability to use dechlorinated tap water to dilute the seawater, saving time and cost over using reverse osmosis water.

Display tank: Reduces the fallow period and doesn’t require a second tank, unless invertebrates are present. Better pH control in most instances. Usually, more saltwater is lost during the process due to the larger aquarium. In established tanks with much microfauna, there may be a significant die-off of algae and small invertebrates. May need to use reverse osmosis water as the dilutant in order to reduce nutrient loading for algae control.

Hyposalinity is really a targeted treatment for marine ich (Cryptocaryon irritans), marine flukes (including Neobenedenia sp.) and has some control over Turbellarian worms (including “black ich”). It does NOT control velvet (Amyloodinium marinum) or clownfish disease, Brooklynella hostilis. There are reports that hyposalinity actually increases the incidence of Uronema, especially in newly acquired fish. Hyposalinity has no direct affect on bacterial, fungal or any internal infections of marine fishes. In rare cases, fish may be infected with brackish water flukes as they travel through the supply chain. In these rare instances, hyposalinity will actually make the disease worse. Experiments have been tried in these cases with “hypersalinity”, holding the fish at higher-than-normal salinity, but results have been poor. In the case of brackish water flukes, praziquantel should be used.

Begin the hyposalinity treatment by determining the final salinity as well as the time and schedule to reach that level. Full hyposalinity is required in order to treat Cryptocaryon, and that equates to a specific gravity of 1.009 at 75 degrees F. or a salinity of 12 parts per thousand. If only Neobenedenia is being controlled, the target can be set a bit higher, to a specific gravity of 1.012 or a salinity of 16 ppt. The time required to reach these endpoints depends on the starting salinity of the tank, as well as the severity of any disease. If severe disease is present, dropping the salinity more quickly, while stressful, starts the treatment faster. Likewise, starting a tank into hyposalinity from a specific gravity of 1.026 will require more time than if the aquarium is already at a lower specific gravity, perhaps 1.022. There is NO firm rule as to how fast to lower the salinity, and some fish simply do not handle hyposalinity as well as others. Inshore fishes tend to handle hyposalinity much better than do deep reef fishes. A general rule of thumb is to reduce the salinity of the aquarium to hyposalinity over 48 hours, in at least four steps. In cases where there is severe disease, hyposalinity should be reached in 24 hours using four steps. Deep reef fish, showing no overt disease and being held at a salinity of 35 ppt might be best lowered in six steps, over 72 hours. It is vital to understand that marine fish can handle a reduction in salinity very well, but the return to normal salinity at the end of the treatment must be done much more slowly. The general recommendation is to return the fish to normal salinity over five days, in at least ten increments. Smaller fish seem more stressed by a rise in salinity than do larger fish. This is likely due to vastly different surface to volume ratios between large and small fish.

During hyposalinity, always monitor the ammonia level as well as the pH to ensure they remain in the proper range. Don’t try to maintain full reef aquarium pH levels during hyposalinity – a slightly lower pH reduces the toxic affect of any ammonia. As long as the aquarium is well aerated, a pH above 7.6 is adequate. Don't raise the water temperature beyond normal. That is a treatment for freshwater ich, not marine ich. 79 degree F. is a good target temperature.

Exactly how to make the salinity adjustments in an accurate fashion requires some mathematical calculations. You need to decide how many days the transition will take, and then how many adjustments you are able to make each day. You then know the number of dilutions you will be making. After that, you need to calculate the change in salinity (in ppt or specific gravity units). You then divide the change in salinity by the number of changes to be made, and that gives the magnitude of each change. However, you really need to recalculate for each change after the first one. Here is an example:

A 20-gallon aquarium at 35 ppt needs to be brought down to 16 ppt over three days. Four adjustments will be made each day, for a total of 12. The change in salinity totals 16 ppt. To make this change in 12 steps, each drop should be 1.33 ppt. Multiply 1.33 by 100 and divide by 35. That equals about 4%. Removing 4% of the tank water and replacing it with freshwater will drop the salinity to 33.7. Repeat the process for each of the next 11 steps. Raising the salinity works in reverse.

When it is all said and done, most people just eyeball the changes as the math becomes pretty convoluted. Raising the salinity can be pretty wasteful if you drain water out of the tank and replace it with slightly more saline water. Many people end up making strong brine solutions and mix that in slowly. Beware though; if you dissolve sea salt at a salinity higher than about 50 ppt, subtle changes can occur, including precipitation of carbonates.

Fish should remain in hyposalinity for 30 days beyond the date that obvious disease symptoms were last seen. Neobenedenia treatments are best to run for 35 days.

###

 

[Seymo44]

@Jay Hemdal Is hypo a safe QT procedure for dragonettes? My primary concern is preventing flukes from entering my display. I am away from home for work too often to effectively use the tank transfer method.

 

[Miami Reef]

Does hypo work well with pyramid butterfly fish?

 

[Jay Hemdal]

Does hypo work well with pyramid butterfly fish?

Yes - I found that hypo is the best way to eliminate Neobendenia from pyramids - praziquantel often fails to work. Interestingly, you do not need to go as low from Neo as you do for ich. Hypo for ich needs to be at a specific gravity of 1.009, while for Neo it just needs to be dropped down to 1.012. I've been told by an expert on Neo that it can be eliminated in less than 20 days of hypo, but I always opt for 30 to 35 days.

Jay

 

[Jay Hemdal]

@Jay Hemdal Is hypo a safe QT procedure for dragonettes? My primary concern is preventing flukes from entering my display. I am away from home for work too often to effectively use the tank transfer method.

The main issue with any quarantine for dragonettes is keeping them well fed during the time spent in the QT. Hyposalinity is fine for them as long as you can keep them well fed.

TTM doesn't work for flukes, even the modified version with peroxide dips often fails. That said, flukes are not a huge issue with dragonettes.

Jay

 

[Miami Reef]

Yes - I found that hypo is the best way to eliminate Neobendenia from pyramids - praziquantel often fails to work. Interestingly, you do not need to go as low from Neo as you do for ich. Hypo for ich needs to be at a specific gravity of 1.009, while for Neo it just needs to be dropped down to 1.012. I've been told by an expert on Neo that it can be eliminated in less than 20 days of hypo, but I always opt for 30 to 35 days.

Jay

Perfect. Question, is it possible for flukes to eradicate itself in the display tank? I haven’t added any fish in months, but I know I used to have flukes because the orange shoulder tang and melanurus wrasse used to itch, and I had pyramids who had the flukes too.

They [orange shoulder and melanurus] haven’t scratched in a long while. I rehomed those previous pyramids.

If the flukes are still in the tank, and I’m going to introduce the pyramid regardless, is he worth prophylactically treating?

 

[Jay Hemdal]

Perfect. Question, is it possible for flukes to eradicate itself in the display tank? I haven’t added any fish in months, but I know I used to have flukes because the orange shoulder tang and melanurus wrasse used to itch, and I had pyramids who had the flukes too.

They [orange shoulder and melanurus] haven’t scratched in a long while. I rehomed those previous pyramids.

If the flukes are still in the tank, and I’m going to introduce the pyramid regardless, is he worth prophylactically treating?

I have had cases of asymptomatic flukes - where the fish had a steady state infection, like they would in the wild, with just a few flukes, not enough to cause active disease. Identifying cases of this are tough because with no symptoms, you don’t go looking for them (grin).
So - I’ve never seen chronic cases of Neobenedenia, but maybe I just didn’t look hard enough?
I’m not sure what to tell you about the pyramid, is this a new one?

Jay

 

[Miami Reef]

I have had cases of asymptomatic flukes - where the fish had a steady state infection, like they would in the wild, with just a few flukes, not enough to cause active disease. Identifying cases of this are tough because with no symptoms, you don’t go looking for them (grin).
So - I’ve never seen chronic cases of Neobenedenia, but maybe I just didn’t look hard enough?
I’m not sure what to tell you about the pyramid, is this a new one?

Jay

Yes, it’s a new one. I decided to treat it with hypo (first time ever using hypo!)

I’m going to assume the orange shoulder and melanurus were scratching from reasons other than flukes - if the pyramid gets flukes after going into the display, and I am positive I did everything correctly, then I’ll assume the fish in the DT reinfected him.

 

[BigIslswlove]

Hyposalinity
Jay Hemdal 2021

This term refers to a long-term bath treatment for marine fishes in which the salt content of the water is lowered and held below the point that certain parasites can survive. The salt level reached, and the time of the treatment are the two variables. Hyposalinity can be used as a primary treatment against certain marine fish diseases (see below) or as a component of an active quarantine for newly acquired fish.

To clarify for beginners: you cannot perform hyposalinity on fish when invertebrates are in the tank. You must isolate the fish to a fish-only situation.

Before instituting a hyposalinity treatment, you need to decide what measurement units you plan on using – salinity or specific gravity. Then, you must have a very accurate measuring device. A laboratory grade hydrometer is best for accurate specific gravity measurements, or to standardize another measurement means. The device employed must be capable of accurately measuring down to one part per thousand, or one specific gravity unit. Better yet is a device that can read to twice that resolution. For example; capable of measuring 16.5 ppt or 1.0125 specific gravity units. Most handheld refractometers are not accurate enough. Swing arm hydrometers can measure this small of a difference, but they must be first checked for accuracy against a laboratory hydrometer.

There are two basic means to administer a hyposalinity treatment: in the display tank or in a quarantine/treatment tank. Invertebrates and some algae cannot survive hyposalinity, so must be removed prior to a hyposalinity treatment (of course, they then need to be cleared of potential disease by use of a proper fallow period). There are benefits and drawbacks to administering hyposalinity in these two modes:

Quarantine tank: Little to no microbiome die-off. Less salt lost. Ability to add other medications during the process if required. System may not be biologically robust enough to manage ammonia levels. Poor pH buffering. Requires a second aquarium and letting the infected display tank go fallow. Ability to use dechlorinated tap water to dilute the seawater, saving time and cost over using reverse osmosis water.

Display tank: Reduces the fallow period and doesn’t require a second tank, unless invertebrates are present. Better pH control in most instances. Usually, more saltwater is lost during the process due to the larger aquarium. In established tanks with much microfauna, there may be a significant die-off of algae and small invertebrates. May need to use reverse osmosis water as the dilutant in order to reduce nutrient loading for algae control.

Hyposalinity is really a targeted treatment for marine ich (Cryptocaryon irritans), marine flukes (including Neobenedenia sp.) and has some control over Turbellarian worms (including “black ich”). It does NOT control velvet (Amyloodinium marinum) or clownfish disease, Brooklynella hostilis. There are reports that hyposalinity actually increases the incidence of Uronema, especially in newly acquired fish. Hyposalinity has no direct affect on bacterial, fungal or any internal infections of marine fishes. In rare cases, fish may be infected with brackish water flukes as they travel through the supply chain. In these rare instances, hyposalinity will actually make the disease worse. Experiments have been tried in these cases with “hypersalinity”, holding the fish at higher-than-normal salinity, but results have been poor. In the case of brackish water flukes, praziquantel should be used.

Begin the hyposalinity treatment by determining the final salinity as well as the time and schedule to reach that level. Full hyposalinity is required in order to treat Cryptocaryon, and that equates to a specific gravity of 1.009 at 75 degrees F. or a salinity of 12 parts per thousand. If only Neobenedenia is being controlled, the target can be set a bit higher, to a specific gravity of 1.012 or a salinity of 16 ppt. The time required to reach these endpoints depends on the starting salinity of the tank, as well as the severity of any disease. If severe disease is present, dropping the salinity more quickly, while stressful, starts the treatment faster. Likewise, starting a tank into hyposalinity from a specific gravity of 1.026 will require more time than if the aquarium is already at a lower specific gravity, perhaps 1.022. There is NO firm rule as to how fast to lower the salinity, and some fish simply do not handle hyposalinity as well as others. Inshore fishes tend to handle hyposalinity much better than do deep reef fishes. A general rule of thumb is to reduce the salinity of the aquarium to hyposalinity over 48 hours, in at least four steps. In cases where there is severe disease, hyposalinity should be reached in 24 hours using four steps. Deep reef fish, showing no overt disease and being held at a salinity of 35 ppt might be best lowered in six steps, over 72 hours. It is vital to understand that marine fish can handle a reduction in salinity very well, but the return to normal salinity at the end of the treatment must be done much more slowly. The general recommendation is to return the fish to normal salinity over five days, in at least ten increments. Smaller fish seem more stressed by a rise in salinity than do larger fish. This is likely due to vastly different surface to volume ratios between large and small fish.

During hyposalinity, always monitor the ammonia level as well as the pH to ensure they remain in the proper range. Don’t try to maintain full reef aquarium pH levels during hyposalinity – a slightly lower pH reduces the toxic affect of any ammonia. As long as the aquarium is well aerated, a pH above 7.6 is adequate. Don't raise the water temperature beyond normal. That is a treatment for freshwater ich, not marine ich. 79 degree F. is a good target temperature.

Exactly how to make the salinity adjustments in an accurate fashion requires some mathematical calculations. You need to decide how many days the transition will take, and then how many adjustments you are able to make each day. You then know the number of dilutions you will be making. After that, you need to calculate the change in salinity (in ppt or specific gravity units). You then divide the change in salinity by the number of changes to be made, and that gives the magnitude of each change. However, you really need to recalculate for each change after the first one. Here is an example:

A 20-gallon aquarium at 35 ppt needs to be brought down to 16 ppt over three days. Four adjustments will be made each day, for a total of 12. The change in salinity totals 16 ppt. To make this change in 12 steps, each drop should be 1.33 ppt. Multiply 1.33 by 100 and divide by 35. That equals about 4%. Removing 4% of the tank water and replacing it with freshwater will drop the salinity to 33.7. Repeat the process for each of the next 11 steps. Raising the salinity works in reverse.

When it is all said and done, most people just eyeball the changes as the math becomes pretty convoluted. Raising the salinity can be pretty wasteful if you drain water out of the tank and replace it with slightly more saline water. Many people end up making strong brine solutions and mix that in slowly. Beware though; if you dissolve sea salt at a salinity higher than about 50 ppt, subtle changes can occur, including precipitation of carbonates.

Fish should remain in hyposalinity for 30 days beyond the date that obvious disease symptoms were last seen. Neobenedenia treatments are best to run for 35 days.

###

Generally, running low salinity all of the time is a mistake. People who do that (stores and some public aquariums) are doing that mostly to control salt costs. Cryptocaryon (ich) can survive a specific gravity of around 1.010, so keeping it any higher is pointless. Fish do not do well long term below 1.011 (like 60+ days) so there is no "sweet spot" for ich. Neobenedenia flukes can be killed at 1.013, and many fish can be held permanently at that specific gravity, so some public aquarium do that, at least for half a year or so.

The big issue is - what if you develop a hypotonic resistant strain of some parasite?

Jay

Thank you Jay! This is working great for the rest of the fish in my 250, as you advised. Ty for the great advise! Hawaii Macros love it too apparently.

 

[Ross]

Jay,

Despite my best efforts I believe a radiant wrasse and leopard wrasse brought flukes into my display.

Their quarantine treatment was HTTM with 6 prazi pro treatments and 2 hydrogen peroxide dips. The radiant continually flashed through quarantine but I trusted that it was just behavioral and flukes couldn’t have possibly survived.

They have been in the display several weeks now and the behavior is the same. I have seen the Midas and one clown scratch once or twice, the other fish have not.

I’m not positive it’s flukes but I think it’s probable. The behavior seems just to be a mild annoyance and not a true heavy infestation. They all eat aggressively and look good other than an occasional scratch.

My question is how risky is trying hypo for flukes with a leopard and radiant wrasse in the tank. I understand they don’t tolerate hypo well, and the situation certainly isn’t dire. I’m not even positive I’m dealing with flukes.

 

[Jay Hemdal]

Jay,

Despite my best efforts I believe a radiant wrasse and leopard wrasse brought flukes into my display.

Their quarantine treatment was HTTM with 6 prazi pro treatments and 2 hydrogen peroxide dips. The radiant continually flashed through quarantine but I trusted that it was just behavioral and flukes couldn’t have possibly survived.

They have been in the display several weeks now and the behavior is the same. I have seen the Midas and one clown scratch once or twice, the other fish have not.

I’m not positive it’s flukes but I think it’s probable. The behavior seems just to be a mild annoyance and not a true heavy infestation. They all eat aggressively and look good other than an occasional scratch.

My question is how risky is trying hypo for flukes with a leopard and radiant wrasse in the tank. I understand they don’t tolerate hypo well, and the situation certainly isn’t dire. I’m not even positive I’m dealing with flukes.

In some cases, flashing/scratching ends up being "behavioral" and not a sign of flukes or other ectoparasites. However, the chance of this being the case when multiple fish show the same behavior is much less. Some wrasse (the radiant perhaps) will look like they are "flashing" on the substrate, but they are actually searching rocks for food. Coris wrasse do this, I don't think that leopards do though.

TTM is not a good solution for flukes, as some species of flukes have adhesive eggs that move right along with the fish. Peroxide dips may knock flukes off (depending on the dose you used) but eggs are not affected at doses less than that which would kill the fish. Praziquantel treatments, properly done, can usually break the fluke life cycle, but again, prazi does not kill fluke eggs. In addition, repeated prazi treatments will cause a group of bacteria to flourish that consume prazi as a food source, so repeated treatments become less and less effective.

I don't know the details of the treatments that you used (dosing, time for each treatment, etc.)

Hyposalinity works very well for most flukes infections, you need to go with half salinity (16 ppt or a specific gravity of 1.012 for 30 days). There are some rare brackish water flukes that survive hyposalinity, but seeing those is quite rare, and seems to be limited to dealer's systems that have been used to house certain brackish water fish (perhaps lookdowns, brackish water mollies and a few others).

Another common cause for fluke treatments to fail is poor biosecurity; leaving a seemingly healthy fish in the tank, while you treat the others, not realizing that this fish, although not showing symptoms, is still harboring flukes is one issue. Moving nets and your hands between tanks can also carry eggs from tank to tank. It has been demonstrated that one Neobenedenia egg can start up a new infection.

Wrasse have no real issues with hyposalinity, but I need to add that leopard wrasse can be delicate and difficult to stabilize in captivity. This is mostly due to their need to feed on small invertebrates in a tank that are typically not present in hypo tanks. The result is that people run hypo with them, the fish dies and they assume it was the hypo, when actually, the fish was going to die anyway.

Jay

 

[Ross]

Thank you Jay. The wrasses are eating frozen, fat, generally look healthy. So I feel I’m passed the stage if getting them stable and adjusted to aquarium life.

Their treatment consisted of 1 5 hour bath at 7.5mg/l then 5 subsequent doses at 2.5mg/l 24 hours before the tank transfer. So it ended up being days 1-5-10-13-16-19. Surely one would think that would break the lifecycle. I’m struggling to see how they could make it through that treatment, but anything is possible I guess.

I have a sample at Aquabiomics that I’m waiting to get back before I make a decision on treating.

 

[Jay Hemdal]

Thank you Jay. The wrasses are eating frozen, fat, generally look healthy. So I feel I’m passed the stage if getting them stable and adjusted to aquarium life.

Their treatment consisted of 1 5 hour bath at 7.5mg/l then 5 subsequent doses at 2.5mg/l 24 hours before the tank transfer. So it ended up being days 1-5-10-13-16-19. Surely one would think that would break the lifecycle. I’m struggling to see how they could make it through that treatment, but anything is possible I guess.

I have a sample at Aquabiomics that I’m waiting to get back before I make a decision on treating.

High dose, short duration prazi treatments like that are an option, but I prefer low dose (2.2 mg/l) as a long bath, and then repeat every 8 days to try and break the life cycle - since you can't kill the eggs, the trick is to try and kill the new flukes when they settle on the fish, but before they grow and lay eggs of their own. The timing for that is a real guess; too many variables (species of fluke and water temperature mostly). I used to tell folks to space the treatment at 9 days, but some flukes were still getting through, so I've been going with 8 days now.

Aquabiomics is a relatively new resource, and the results still need to be reviewed for efficacy. This is really similar to ICP testing, you need to use that as a tool, but not rely on the results to 100% drive your course of action.

Jay

 

[Australian_Reef]

Just don’t do the stupid thing I did many years ago in my first hypo period. I removed all inverts from my main tank and dropped the salinity. Then realised how many unseen inverts are in there.. from sponges, to worms etc etc. quickly had a much worse problem. Really stupid and I should have known better. But when you panic and you are short on time you make bad choices.

Lesson learned.

 

[GARRIGA]

Why not take a tank and fill it half way to 24 ppt. Add fish then remove water and replace with RODI that has Kent Marine RO Right at the desired rate to effect 12 ppt. Now I have an ATO maintain that water level and assist that process by placing a tight but not air tight lid reducing evaporation. To reverse the process. Add SW until filling the tank returning salinity to 24 ppt continue QT or start with a lower water level if need is 35 ppt. Key is using a predefined water level which is easier to monitor by eye balling as a second confirmation salinity running that razor edge most likely stable. Obviously salt creep need ms to be reintroduced to tank water but that will likely be contained to tank sides depending on water motion. Another advantage to having a tank taller than water level.

For ammonia control advanced oxidation process will convert that to nitrates. Easier to execute with ozone since that’s a gas vs dripping peroxide since goal is reduced evaporation to maintain a stable 12 ppt.

As for pH. How low is high enough. Meaning will saltwater fish expire during this treatment were pH 6 or lower? Fish transported from overseas I recall receiving at under 7 and only effects were opening bag and suddenly releasing its co2 raising pH and converting ammonium to ammonia. Perhaps maintaining below pH equilibrium removes the need to worry about ammonia and just run sediment filtration to keep water clear for observation. Fish seemed fine otherwise sitting in less than 7 pH which was done by moving them quickly to fresh SW that was lowered to that pH then that water slowly acclimated to central system parameters. Recall few fish losses doing that if any.

Another option is running an undergravel filter naked without substrate drawing majority of pathogen into the filtration where the UV-C dissipates the catalyst used and help accelerate the reduction of pathogens before treatment started and post should treatment be halted suddenly because fish showed stress.

Going to be testing this therefore not just pie in the sky ideas but logically speaking makes sense. My biggest fear is evaporation dropping the 12 ppt to lethal fir not just pathogens but their host we are trying to save.

Also going to find some brackish plants therefore create perhaps a sealed tank and completely eliminate evaporation allowing that plant lit 24/7 to handle gas exchange. Opening lid only to feed or further medicate and that can be further advanced by having a custom lid with small ports. Plus having tank lid with full spectrum will allow better observation of fish. Would also solve the worries of ammonium although any medication used during this process can’t be detrimental to that plant. Mangroves likely what most will think of and available in the hobby, very robust being they evolved to handle changing salinity. We catch bass in the same waters we catch brackish fir amongst the mangroves because top layer different salinity for example. Gonna likely need a lot of mangroves but guessing might be other macro algae that evolved in that environment which might be more practical.

I know. That’s a lot to process but that’s how progress evolves. Good for thought.

Probably got the lowering and raising of water wrong since it’s early but the main point being lowering and raising my easiest approach to changing salinity. Like I said. It’s early

 

[youclowntoomuch]

Hyposalinity
Jay Hemdal 2021

This term refers to a long-term bath treatment for marine fishes in which the salt content of the water is lowered and held below the point that certain parasites can survive. The salt level reached, and the time of the treatment are the two variables. Hyposalinity can be used as a primary treatment against certain marine fish diseases (see below) or as a component of an active quarantine for newly acquired fish.

To clarify for beginners: you cannot perform hyposalinity on fish when invertebrates are in the tank. You must isolate the fish to a fish-only situation.

Before instituting a hyposalinity treatment, you need to decide what measurement units you plan on using – salinity or specific gravity. Then, you must have a very accurate measuring device. A laboratory grade hydrometer is best for accurate specific gravity measurements, or to standardize another measurement means. The device employed must be capable of accurately measuring down to one part per thousand, or one specific gravity unit. Better yet is a device that can read to twice that resolution. For example; capable of measuring 16.5 ppt or 1.0125 specific gravity units. Most handheld refractometers are not accurate enough. Swing arm hydrometers can measure this small of a difference, but they must be first checked for accuracy against a laboratory hydrometer.

There are two basic means to administer a hyposalinity treatment: in the display tank or in a quarantine/treatment tank. Invertebrates and some algae cannot survive hyposalinity, so must be removed prior to a hyposalinity treatment (of course, they then need to be cleared of potential disease by use of a proper fallow period). There are benefits and drawbacks to administering hyposalinity in these two modes:

Quarantine tank: Little to no microbiome die-off. Less salt lost. Ability to add other medications during the process if required. System may not be biologically robust enough to manage ammonia levels. Poor pH buffering. Requires a second aquarium and letting the infected display tank go fallow. Ability to use dechlorinated tap water to dilute the seawater, saving time and cost over using reverse osmosis water.

Display tank: Reduces the fallow period and doesn’t require a second tank, unless invertebrates are present. Better pH control in most instances. Usually, more saltwater is lost during the process due to the larger aquarium. In established tanks with much microfauna, there may be a significant die-off of algae and small invertebrates. May need to use reverse osmosis water as the dilutant in order to reduce nutrient loading for algae control.

Hyposalinity is really a targeted treatment for marine ich (Cryptocaryon irritans), marine flukes (including Neobenedenia sp.) and has some control over Turbellarian worms (including “black ich”). It does NOT control velvet (Amyloodinium marinum) or clownfish disease, Brooklynella hostilis. There are reports that hyposalinity actually increases the incidence of Uronema, especially in newly acquired fish. Hyposalinity has no direct affect on bacterial, fungal or any internal infections of marine fishes. In rare cases, fish may be infected with brackish water flukes as they travel through the supply chain. In these rare instances, hyposalinity will actually make the disease worse. Experiments have been tried in these cases with “hypersalinity”, holding the fish at higher-than-normal salinity, but results have been poor. In the case of brackish water flukes, praziquantel should be used.

Begin the hyposalinity treatment by determining the final salinity as well as the time and schedule to reach that level. Full hyposalinity is required in order to treat Cryptocaryon, and that equates to a specific gravity of 1.009 (temperature calibrated at 75 degrees F.) or a salinity of 12 parts per thousand. If only Neobenedenia is being controlled, the target can be set a bit higher, to a specific gravity of 1.012 or a salinity of 16 ppt. The time required to reach these endpoints depends on the starting salinity of the tank, as well as the severity of any disease. If severe disease is present, dropping the salinity more quickly, while stressful, starts the treatment faster. Likewise, starting a tank into hyposalinity from a specific gravity of 1.026 will require more time than if the aquarium is already at a lower specific gravity, perhaps 1.022. There is NO firm rule as to how fast to lower the salinity, and some fish simply do not handle hyposalinity as well as others. Inshore fishes tend to handle hyposalinity much better than do deep reef fishes. A general rule of thumb is to reduce the salinity of the aquarium to hyposalinity over 48 hours, in at least four steps. In cases where there is severe disease, hyposalinity should be reached in 24 hours using four steps. Deep reef fish, showing no overt disease and being held at a salinity of 35 ppt might be best lowered in six steps, over 72 hours. It is vital to understand that marine fish can handle a reduction in salinity very well, but the return to normal salinity at the end of the treatment must be done much more slowly. The general recommendation is to return the fish to normal salinity over five days, in at least ten increments. Smaller fish seem more stressed by a rise in salinity than do larger fish. This is likely due to vastly different surface to volume ratios between large and small fish.

During hyposalinity, always monitor the ammonia level as well as the pH to ensure they remain in the proper range. Don’t try to maintain full reef aquarium pH levels during hyposalinity – a slightly lower pH reduces the toxic affect of any ammonia. As long as the aquarium is well aerated, a pH above 7.6 is adequate. Don't raise the water temperature beyond normal. That is a treatment for freshwater ich, not marine ich. 79 degree F. is a good target temperature.

Exactly how to make the salinity adjustments in an accurate fashion requires some mathematical calculations. You need to decide how many days the transition will take, and then how many adjustments you are able to make each day. You then know the number of dilutions you will be making. After that, you need to calculate the change in salinity (in ppt or specific gravity units). You then divide the change in salinity by the number of changes to be made, and that gives the magnitude of each change. However, you really need to recalculate for each change after the first one. Here is an example:

A 20-gallon aquarium at 35 ppt needs to be brought down to 16 ppt over three days. Four adjustments will be made each day, for a total of 12. The change in salinity totals 16 ppt. To make this change in 12 steps, each drop should be 1.33 ppt. Multiply 1.33 by 100 and divide by 35. That equals about 4%. Removing 4% of the tank water and replacing it with freshwater will drop the salinity to 33.7. Repeat the process for each of the next 11 steps. Raising the salinity works in reverse.

When it is all said and done, most people just eyeball the changes as the math becomes pretty convoluted. Raising the salinity can be pretty wasteful if you drain water out of the tank and replace it with slightly more saline water. Many people end up making strong brine solutions and mix that in slowly. Beware though; if you dissolve sea salt at a salinity higher than about 50 ppt, subtle changes can occur, including precipitation of carbonates.

Fish should remain in hyposalinity for 30 days beyond the date that obvious disease symptoms were last seen. Neobenedenia treatments are best to run for 35 days.

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I have a 15 g tank. Im looking to do hyposalinity , but I only have access to distilled store bought water. Are there any special stipulations that I have to follow/ watch?

 

[Jay Hemdal]

I have a 15 g tank. Im looking to do hyposalinity , but I only have access to distilled store bought water. Are there any special stipulations that I have to follow/ watch?

Why not just use tap water? If you have municipal water, that would be fine.

 

[youclowntoomuch]

Why not just use tap water? If you have municipal water, that would be fine.

I’ve read bad things. Is there a mixing solution that you’d recommend? I currently have the purple bag of instant ocean. Is there anything else I need to add?

 

[Jay Hemdal]

I’ve read bad things. Is there a mixing solution that you’d recommend? I currently have the purple bag of instant ocean. Is there anything else I need to add?

Instant Ocean already contains some dechlorinator, but if your city water has a lot of chlorine in it, you could add some more dechlor. Otherwise, tap water is fine. I actually prefer it because I can adjust the hot and cold taps and immediately get the desired temperature.

 

[youclowntoomuch]

Instant Ocean already contains some dechlorinator, but if your city water has a lot of chlorine in it, you could add some more dechlor. Otherwise, tap water is fine. I actually prefer it because I can adjust the hot and cold taps and immediately get the desired temperature.

Hello Jay, Ive begun the hypo process and will achieve 1.009 in the next couple of days. My gramma is starting to flash again and so is my tailspot blenny. Is there anything else I can add to give the fish relief during this time? I added some herbtana but Ive not seem much positive press on that solution. Thanks in advance