7 month old tank depleting magnesium, alkalinity going up without dosing, corals dying. Synthetic rock doing something?

[jassojasso]

Hi!
I am completely at loss with my tank. I set up a 185 gallon tank in May -24. It was an upgrade for my old 65 gallon which I transferred ~ 60 pounds of live rock and fish to the new tank. Old tank was thriving, I was dosing all for reef which kept everything pretty much in check.
I transfered all old rock to new tank and added additional ~ 70 pounds of synthetic Aquaforest Reef rock.
Im doing ~ 7% water changes every week with salt mix that mixes to 1350 ppm magnesium and 8,5 dkh alkalinity, 420 calcium. I have tested newly mixed salt water multiple times and values are correct.
First few months everything was doing fine but after that I slowly lost all my SPS to browning/STN etc. At that time my magnesium started to quickly deplete. I started to dose magnesium chloride hexahydrate and have to dose it a lot to keep the magnesium at check. Magnesium can drop from 1350 to 1200 in one week if I dont dose it. Calcium is pretty stable.
I am not dosing any alkalinity but it creeps up to 9-10dKh between water changes which brings it down closer to 9. NO3 and PO4 have been pretty constant being around 10 and 0,08 ish.
I have checked the sand bed (it is really shallow) and all the equipment to see if there is precipitation but I have not seen any.
Now I have started to lose LPS that have been doing fine for years in the old tank. I did an ICP which is below.
I am completely at loss with this tank and my problems. I cant figure anything else than synthetic rock is doing something weird. I have read few reports where AF rock has increased alkalinity on its own but what the heck is happening to magnesium?
I have no algae, cyano, dinos or anything else screwy going on. All the rock is covered in coraline algea and looks pretty good.
I am strongly pondering getting the synthetic rock out and replacing it with dead live rock.
Any suggestions?

 

[Randy Holmes-Farley]

Magnesium can drop from 1350 to 1200 in one week if I dont dose it. Calcium is pretty stable.
I am not dosing any alkalinity but it creeps up to 9-10dKh between water changes which brings it down closer to 9. NO3 and PO4 have been pretty constant being around 10 and 0,08 ish.

That is test error, salinity declines, or due to water changes with a terribly low magnesium mix.

There is no possibility that a tank with no significant calcium or alk consumption has detectable magnesium consumption.

I’d recommend using your kit on some new salt water, and switching over to RMM:

Just say NO to magnesium testing: RMM is born

OK, this thread has been many years in the making, and I'm posting it here since folks in the chem forum are probably already tired of all the threads relating to problematic magnesium testing. I'm going to propose a method, let's call it the Randy Magnesium Method, or RMM for short. All good...

www.reef2reef.com

 

[Randy Holmes-Farley]

The synthetic rock can certainly be releasing some alk. That's a known issue in many cases. If alk gets too high, there are ways to lower it in new salt water, or more risky, lowering it in the tank.

 

[Reef-Mart]

If you’re using AF test kits that may be your problem. The test kits I’ve used from them recently have been way off.

 

[jassojasso]

I appriciate the answers.
I have been using salifert test kits. I have used multiple different set of kits with similar results. Also I have tested the new salt water. Icp shows mg of 1330 (normal) after I have dosed significant amount of magnesium chloride. I have another small 20 gallon tank on which I do water changes with same salt water. It always tests same 1350 which is in salt mix (so no consumption) while my big tank depletes it for some very mysterious reason
I underatand that testing error is the most logical explanation but the icp speaks against it.
I wouldnt be overly worried about this but my corals are slowly dying off and I think there is something wrong with the water. Also the problems started with corals before I started to dose magnsesium

 

[Pod_01]

Just my opinion, you may have multiple things happening.
Do you have pictures of your sps when this happened:

First few months everything was doing fine but after that I slowly lost all my SPS to browning/STN etc.

For example when I experienced PO4 starvation some SPS looked like this:

Once I stopped artificially lowering my PO4 stopped using phosphate binders GFO etc… things improved.

It did take 3+ months to get there.

From my experience SPS can have negative response to sinking PO4. Especially if it go from 0.07 to 0.02ppm.

Good luck,

 

[jassojasso]

Just my opinion, you may have multiple things happening.
Do you have pictures of your sps when this happened:


For example when I experienced PO4 starvation some SPS looked like this:

Once I stopped artificially lowering my PO4 stopped using phosphate binders GFO etc… things improved.

It did take 3+ months to get there.

From my experience SPS can have negative response to sinking PO4. Especially if it go from 0.07 to 0.02ppm.

Good luck,

Hi.
First my purple stylo and seriatopora stned out in span of 2-3 months. Then my bali green slimer started to turn brown and in 2 months it browned out and then rest of the flesh stripped off. My pavona turned brown and died on all the parts that faced the light.
I have not used gfo.
I only run carbon, have small refugium and dose magnesium and very occasionally Ca-chloride. I have not had any need to dose alkalinity (since it is going up)
Lately I have had hammer corals losing entire heads by polyp bailout.
Leathers and zoas doing mostly fine

 

[Randy Holmes-Farley]

I appriciate the answers.
I have been using salifert test kits. I have used multiple different set of kits with similar results. Also I have tested the new salt water. Icp shows mg of 1330 (normal) after I have dosed significant amount of magnesium chloride. I have another small 20 gallon tank on which I do water changes with same salt water. It always tests same 1350 which is in salt mix (so no consumption) while my big tank depletes it for some very mysterious reason
I underatand that testing error is the most logical explanation but the icp speaks against it.
I wouldnt be overly worried about this but my corals are slowly dying off and I think there is something wrong with the water. Also the problems started with corals before I started to dose magnsesium

I’m not convinced and the icp does not prove anything except it was fine when tested.

How much of what exactly are you dosing?

 

[Randy Holmes-Farley]

Hi.
First my purple stylo and seriatopora stned out in span of 2-3 months. Then my bali green slimer started to turn brown and in 2 months it browned out and then rest of the flesh stripped off. My pavona turned brown and died on all the parts that faced the light.
I have not used gfo.
I only run carbon, have small refugium and dose magnesium and very occasionally Ca-chloride. I have not had any need to dose alkalinity (since it is going up)

The alk rise may be the source of the problems:

Is it possible for Alkalinity to rise in a stable system by adding Aquaforest man made rock to sump?

Ok, I know this sounds crazy. I can hear it already, believe me. Almost didn’t even want to post this. I have a fairly mature mixed reef tank that has been stable for a long time. Nothing more than minor swings over years. The refugium section of my sump has been unused and empty for years. On...

www.reef2reef.com

 

[A_Blind_Reefer]

I find these product claims interesting….

“The rock will continuously support filtration processes, stabilize parameters and facilitate the development of marine life.”

“It stabilizes the pH and KH of water, which greatly facilitates the calcification of skeletons and allows faster growth of corals, which in stable parameters build harder and healthier skeletons.”


I personally did not notice any change with magnesium myself. Just skyrocketing Alk and some mild ph swings. I did/still do have some stn events but I think that was an underlying bacterial issue, which was allowed to take hold when things were aggravated by a large Alk swing, but that is just a theory. I am curious to see what’s going on with your system though so I’m following along.

Edit. I do find it interesting that your stn events have been going on for months as well. I’m still struggling with mine and have lost a few pieces.

 

[A_Blind_Reefer]

Oh, and I’m still holding my breath waiting for af to clarify these claims and how they’re possible….

 

[jassojasso]

I’m not convinced and the icp does not prove anything except it was fine when tested.

How much of what exactly are you dosing?

I am dosing magnesium chloride hexahydrate MgCl2 about 100 grams (dry product) per week. This keeps my mg levels at 1350 (same my salt mix mixes at)

 

[jassojasso]

I find these product claims interesting….

“The rock will continuously support filtration processes, stabilize parameters and facilitate the development of marine life.”

“It stabilizes the pH and KH of water, which greatly facilitates the calcification of skeletons and allows faster growth of corals, which in stable parameters build harder and healthier skeletons.”


I personally did not notice any change with magnesium myself. Just skyrocketing Alk and some mild ph swings. I did/still do have some stn events but I think that was an underlying bacterial issue, which was allowed to take hold when things were aggravated by a large Alk swing, but that is just a theory. I am curious to see what’s going on with your system though so I’m following along.

Edit. I do find it interesting that your stn events have been going on for months as well. I’m still struggling with mine and have lost a few pieces.

I think I will just rip off the AF stone out and replace it with dead live rock that I started my first tank with. I still have over 30kg/70ish pounds of matured live rock from previous tank and sandbed so I think my nitrifying bacteria will be fine. I already lost all the sensitive corals so I dont have anything to lose

 

[Randy Holmes-Farley]

I am dosing magnesium chloride hexahydrate MgCl2 about 100 grams (dry product) per week. This keeps my mg levels at 1350 (same my salt mix mixes at)

What size tank? What brand?

 

[jassojasso]

What size tank? What brand?

Total water volume is 200 gallons. It is Triton magnesium.

MgCl2

The most experienced in solution based water chemistry in the industry. Continuing to revolutionise reef keeping worldwide since 2008.

www.triton-reagents.de

I am wondering if it all is just percipitating somewhere… I have looked high and low and havent found any deposits

 

[A_Blind_Reefer]

I am dosing magnesium chloride hexahydrate MgCl2 about 100 grams (dry product) per week. This keeps my mg levels at 1350 (same my salt mix mixes at)

Are you making a solution with rodi, or just dumping the powder in the tank?

 

[jassojasso]

Are you making a solution with rodi, or just dumping the powder in the tank?

Mixing it to RODI dosing to sump in high flow area

 

[A_Blind_Reefer]

Mixing it to RODI dosing to sump in high flow area

Just had to clarify….you never know.

 

[Randy Holmes-Farley]

I’ve been down this road dozens of times with other reefers. There is NO explanation other than the ones I gave.

I think you have a math error, which I note in the last paragraph below.

Sure, magnesium can precipitate, but to precipitate 150 ppm of magnesium in a week would likely consume more than 1500 ppm of calcium and more than 200 dKH of alk, to make the material that normally precipitates from seawater. Even if somehow you managed to make pure magnesium carbonate, that would have required depletion of 35 dKH of alk.

You say to maintain magnesium, you dosed 100 dry grams of magnesium chloride hexahydrate to 200 gallons. That only boost magnesium by 16 ppm. Most kits can just barely see that boost. thsts a far, far cry from claiming a 150 ppm drop in a week.

 

[jassojasso]

I’ve been down this road dozens of times with other reefers. There is NO explanation other than the ones I gave.

I think you have a math error, which I note in the last paragraph below.

Sure, magnesium can precipitate, but to precipitate 150 ppm of magnesium in a week would likely consume more than 1500 ppm of calcium and more than 200 dKH of alk, to make the material that normally precipitates from seawater. Even if somehow you managed to make pure magnesium carbonate, that would have required depletion of 35 dKH of alk.

You say to maintain magnesium, you dosed 100 dry grams of magnesium chloride hexahydrate to 200 gallons. That only boost magnesium by 16 ppm. Most kits can just barely see that boost. thsts a far, far cry from claiming a 150 ppm drop in a week.

Thanks for your input. I appriciate it and consider you far greater expert on the matter and absolutely trust your calculations. Perhaps magnesium and its level is just a stray path that I focused on while trying to solve my problems. Maybe it is the leaching alkalinity (and maybe something else unmeasurable) from the synthetic rock which is causing problems with my tank.