pH effect on phosphate

[Stoney]

I've noticed that lower pH in my tank consistently leads to lower phosphate measurements as well. Wondering if anyone else has experienced this and if so, is this just a result of how the hanna phosphate test kits work? Or are the corals actually experiencing a lower phosphate level? Thanks for any insight.

 

[KrisReef]

I've noticed that lower pH in my tank consistently leads to lower phosphate measurements as well. Wondering if anyone else has experienced this and if so, is this just a result of how the hanna phosphate test kits work? Or are the corals actually experiencing a lower phosphate level? Thanks for any insight.

I don't really "know", but if you are making a correct observation it is conceivable that phosphate is less soluble in lower pH solutions. The test kit measures water concentrations and not the amount of phosphate that is adhered to the rock and substrates.

How much does your pH move about during the day? Some folk recommend testing the same time each day to avoid measuring daily movements but to capture trends across days. ( I hope that made sense?) I try to measure before I feed in the afternoon myself. The phosphates always are higher immediately after I feed but I don't monitor pH and rarely measure for it.

Lets see what other folk have to say. Someone on here "knows" the solubility of phosphates at temperature and pH changes.

 

[Stoney]

I don't really "know", but if you are making a correct observation it is conceivable that phosphate is less soluble in lower pH solutions. The test kit measures water concentrations and not the amount of phosphate that is adhered to the rock and substrates.

How much does your pH move about during the day? Some folk recommend testing the same time each day to avoid measuring daily movements but to capture trends across days. ( I hope that made sense?) I try to measure before I feed in the afternoon myself. The phosphates always are higher immediately after I feed but I don't monitor pH and rarely measure for it.

Lets see what other folk have to say. Someone on here "knows" the solubility of phosphates at temperature and pH changes.

My pH usually swings from 8 - 8.4 throughout the day and yea I measure at the same time everyday +-10 mins or so. I also weigh out food to the nearest mg to keep phosphate stable.

I've found that keeping my windows closed for too long and pH maxing out under 8.3 can drastically lower phosphate from around 30ppb to 10ppb temporarily. Good point about the solubility. Just didnt expect it to make such a big difference! But I guess phosphate concentrations are pretty low to begin with.

 

[KrisReef]

Ok, SO you made me look;

pH And The Reef Aquarium

For many aquarists, pH is not something that they have much experience with aside from their aquarium. For many, pH is almost a black box measurement: something to be considered, but whose physical meaning makes little sense to them. This...

www.reef2reef.com

Phosphate in the Reef Aquarium

The phosphorus atom is one of living matter’s basic building blocks. It is present in every living creature and in the water of every reef aquarium. Unfortunately, it is often present in excess in reef aquaria and that excess has the potential to...

www.reef2reef.com

One possible mechanism could be through calcium phosphate precipitation, as outlined above. A second mechanism for potential phosphate reduction when using high pH additives is the binding of phosphate to calcium carbonate surfaces. The absorption of phosphate from seawater onto aragonite is pH dependent, with the binding maximized at around pH 8.4 and with less binding occurring at lower and higher pH values.

@Randy Holmes-Farley -I'm guessing?

 

[reefluvrr]

I've noticed that lower pH in my tank consistently leads to lower phosphate measurements as well.

Do you carbon dose and/or add bacteria in your tank?

Recently whenever my PO4 have climbed up beyond 0.12 I would add bacteria to my tank for carbon dosing reasons.
Within 12 hours my PO4 drops as well as my pH by 0.1.

 

[Stoney]

Do you carbon dose and/or add bacteria in your tank?

Recently whenever my PO4 have climbed up beyond 0.12 I would add bacteria to my tank for carbon dosing reasons.
Within 12 hours my PO4 drops as well as my pH by 0.1.

Good thinking, but no I dont do any carbon dosing. Only things I dose are soda ash, calcium chloride, magnesium chloride, and sodium nitrate.

Honestly surprised no one else has observed this. It's not something that happens occasionally, it happens every single time indoor CO2 gets too high. Starting to think this might be responsible for some of those unexplained events.

 

[Dan_P]

I've noticed that lower pH in my tank consistently leads to lower phosphate measurements as well. Wondering if anyone else has experienced this and if so, is this just a result of how the hanna phosphate test kits work? Or are the corals actually experiencing a lower phosphate level? Thanks for any insight.

Can you provide the PO4 test results that you observed to change with the pH?

 

[Stoney]

Can you provide the PO4 test results that you observed to change with the pH?

I have all the PO4 measurements, but my apex jr only saves the last 7 days of pH. I could post them anyways if you'd like. I also dont test daily these days (2-3 times/week), but I did for a period of 9 months. I was trying to stabilize PO4 by adjusting food input down to the mg, but it just wouldnt stop fluctuating. It's the only parameter that I havent been able to nail down, but keeping CO2 stable at atmospheric levels has helped a lot.

And in case anyone is considering testing error, back to back tests are always within 5ppb. I even get the exact same number occasionally. I've performed the test hundreds of times, probably getting close to 1000 at this point.

 

[Randy Holmes-Farley]

What sort of range of pH and phosphate are you talking about, and are you referring to diurnal fluctuations (within a day), or comparing over a more extended period?

I've not seen anyone else not a relationship and cannot think why there would be one, except that at higher pH, both biological and abiotic calcification is faster, and phosphate may tend to get incorporated into the precipitating calcium carbonate.

 

[Stoney]

What sort of range of pH and phosphate are you talking about, and are you referring to diurnal fluctuations (within a day), or comparing over a more extended period?

I've not seen anyone else not a relationship and cannot think why there would be one, except that at higher pH, both biological and abiotic calcification is faster, and phosphate may tend to get incorporated into the precipitating calcium carbonate.

My pH typically fluctuates 8 - 8.4 throughout the day, but when it starts to peak under 8.3, phosphorus can go from 20-30 ppb down to 10 ppb. I've even had it drop near zero before, but I've learned not to panic and just make sure ambient CO2 matches atmospheric. This is day to day variations, testing at the same time.

Right, that's why I was wondering if maybe the hanna phosphate test is pH dependent and whether the corals are even seeing the PO4 fluctuations. I do notice bounce mushrooms deflating and some zoas closing up but havent noticed any reaction from sps and euphyllia.

 

[Dan_P]

I have all the PO4 measurements, but my apex jr only saves the last 7 days of pH. I could post them anyways if you'd like. I also dont test daily these days (2-3 times/week), but I did for a period of 9 months. I was trying to stabilize PO4 by adjusting food input down to the mg, but it just wouldnt stop fluctuating. It's the only parameter that I havent been able to nail down, but keeping CO2 stable at atmospheric levels has helped a lot.

And in case anyone is considering testing error, back to back tests are always within 5ppb. I even get the exact same number occasionally. I've performed the test hundreds of times, probably getting close to 1000 at this point.

I would be interested in seeing the pH and PO4 numbers but if it requires a big effort, I won't impose on you.

Dan

 

[Stoney]

I would be interested in seeing the pH and PO4 numbers but if it requires a big effort, I won't impose on you.

Dan

Not at all, it's become almost second nature at this point so I want to make sure it isnt confirmation bias. Also have a second tank with a classic apex that might have caught something, but it has algae issues so PO4 isnt as stable. I'll start taking daily PO4 measurements on the main tank and saving pH logs. Might take awhile to capture one of those events since I'd rather not do it on purpose. I'll post back when I have some clean data.

 

[homer1475]

I test the same time twice a week. My PO4 is pretty consistent between 0.13 to 0.19. I control this with very precise GFO input(3TBS changed weekly keeps me in those numbers). My PH on the other hand can be anywhere from 7.74 to 8.01 during the day.

Never noticed any difference whether my PH is in the 8 range or the high 7 range. PO4 always measures where I think it should be.

I often get weird reading from the ULR phosphorus checker, just chalk that up to a fingerprint, smear on the glass, particle floating in the water, etc, etc. Run another test back to back, and the second usually is where it should be.

Have you tested back to back to rule out test error?

 

[Garf]

Good thinking, but no I dont do any carbon dosing. Only things I dose are soda ash, calcium chloride, magnesium chloride, and sodium nitrate.

Honestly surprised no one else has observed this. It's not something that happens occasionally, it happens every single time indoor CO2 gets too high. Starting to think this might be responsible for some of those unexplained events.

Is there a any correlation between adding nitrate and phosphate reduction, by any chance? Photosynthesis is driving the increase in pH I assume, consuming both N & P, along with other stuff.

 

[Stoney]

I often get weird reading from the ULR phosphorus checker, just chalk that up to a fingerprint, smear on the glass, particle floating in the water, etc, etc. Run another test back to back, and the second usually is where it should be.

Have you tested back to back to rule out test error?

Yup, I always do a second test to verify if the result is unexpected. Usually get within 5ppb of the first measurement. Actually just got 47ppb twice in a row. It's surprisingly precise at times.

Is there a any correlation between adding nitrate and phosphate reduction, by any chance? Photosynthesis is driving the increase in pH I assume, consuming both N & P, along with other stuff.

Not that I can tell, I dose NO3 daily at the same time and only get these PO4 drops occasionally. Looking back at my logs it happens on average once every other month. That's the thing, its actually the opposite where lower pH is correlated with lower PO4. I usually can't test any difference in NO3.

 

[Garf]

Yup, I always do a second test to verify if the result is unexpected. Usually get within 5ppb of the first measurement. Actually just got 47ppb twice in a row. It's surprisingly precise at times.



Not that I can tell, I dose NO3 daily at the same time and only get these PO4 drops occasionally. Looking back at my logs it happens on average once every other month. That's the thing, its actually the opposite where lower pH is correlated with lower PO4. I usually can't test any difference in NO3.

Sometimes crap just happens. It makes it fun, lol. If we knew everything it would be boring

 

[East1]

Yup, I always do a second test to verify if the result is unexpected. Usually get within 5ppb of the first measurement. Actually just got 47ppb twice in a row. It's surprisingly precise at times.



Not that I can tell, I dose NO3 daily at the same time and only get these PO4 drops occasionally. Looking back at my logs it happens on average once every other month. That's the thing, its actually the opposite where lower pH is correlated with lower PO4. I usually can't test any difference in NO3.

I just found this thread specifically because I was searching for info about my hannah phosphate tests. I recently added an air input from outside and it took my pH from a max of 7.9 to a max of 8.4 consistently, it's only been a week but I keep strong logs of my nutrient testing and in the week my phosphate has basically tripled (from .08 to .4 or so, I've done multiple hanna phosphate tests and they come back consistent. So far I've not noticed a difference in corals despite this, though.


Edit:

Phosphate in the Reef Aquarium

The phosphorus atom is one of living matter’s basic building blocks. It is present in every living creature and in the water of every reef aquarium. Unfortunately, it is often present in excess in reef aquaria and that excess has the potential to...

www.reef2reef.com

this thread seems to explain it a little, it seems this might also explain my change in cyano over time as organic phosphate is solubilised as inorganic phosphate making it inaccessible to cyano vs regular algae.

 

[Randy Holmes-Farley]

this thread seems to explain it a little, it seems this might also explain my change in cyano over time as organic phosphate is solubilised as inorganic phosphate making it inaccessible to cyano vs regular algae.

What specifically in the article are you referring to?

 

[East1]

What specifically in the article are you referring to?

The section on protionation, and the species as function of pH - perhaps the way colormetric tests work is affected by this in some way because my corals didn't show any reaction to what was suddenly a huge change in Phosphate, when the only change to the tank chemically was adding an outside air line to the skimmer, which raised the pH substantially.

So I assume the species changes how the Hanna test reacts as opposed to sudden spikes in actual phosphate.

The last bit was pure conjecture, perhaps the skew in species of inorganic phosphates is part of a wider change of the distribution of P compounds in the reef or something to this effect. Accompanying the change in what my tests pick up I've noticed a reduction of 'crud' in the bottom of the tank, too.

 

[Randy Holmes-Farley]

The section on protionation, and the species as function of pH - perhaps the way colormetric tests work is affected by this in some way because my corals didn't show any reaction to what was suddenly a huge change in Phosphate, when the only change to the tank chemically was adding an outside air line to the skimmer, which raised the pH substantially.

So I assume the species changes how the Hanna test reacts as opposed to sudden spikes in actual phosphate.

The last bit was pure conjecture, perhaps the skew in species of inorganic phosphates is part of a wider change of the distribution of P compounds in the reef or something to this effect. Accompanying the change in what my tests pick up I've noticed a reduction of 'crud' in the bottom of the tank, too.

Hanna won't respond to typical organic phosphates, but it will respond to all forms of inorganic orthophosphate, regardless of pH because the test kit itself changes the pH for the test and converts them all to the same form.