Large daily PO4 swings

[Ziggy17]

As the title suggests.

The past week or so, maybe 10 days, I’ve been testing my PO4 at 6pm and then at 7am and I’m seeing large swings. On average 0.7 in the evening and under 0.1 in the AM. I don’t have any macros and the skimmer is on 24/7. I don’t feed heavy. 3 times a day they get a tweezer pinch of frozen brine and a tweezer pinch of mysis. I’ve changed the battery in the Hannah checker and the process is identical for every test. NO3 remains steady at 18-20 during this 10 day period. Without any intervention I wouldn’t have thought this was possible, but I’ve replicated the results daily for over a week. Tank has a total volume of 143g so it’s large enough to not expect daily nutrient swings of this nature.

Any ideas what’s causing this?

 

[lapin]

Perhaps something is consuming it at night. Or. Something is releasing it when the lights are on. Puzzled?

 

[Dan_P]

As the title suggests.

The past week or so, maybe 10 days, I’ve been testing my PO4 at 6pm and then at 7am and I’m seeing large swings. On average 0.7 in the evening and under 0.1 in the AM. I don’t have any macros and the skimmer is on 24/7. I don’t feed heavy. 3 times a day they get a tweezer pinch of frozen brine and a tweezer pinch of mysis. I’ve changed the battery in the Hannah checker and the process is identical for every test. NO3 remains steady at 18-20 during this 10 day period. Without any intervention I wouldn’t have thought this was possible, but I’ve replicated the results daily for over a week. Tank has a total volume of 143g so it’s large enough to not expect daily nutrient swings of this nature.

Any ideas what’s causing this?

I am stumped.

The phosphate test results can be pushed high by suspended particles.

 

[Ziggy17]

I am stumped.

The phosphate test results can be pushed high by suspended particles.

Last feed time is 2 hours prior to evening test to eliminate that issue. I’m stumped as well.

 

[EnterName]

This still feels like an absolute stretch as a difference of 0.6ppm is absolutely insane, but are you dosing anything that might cause phosphate precipitation or a pH change? CaCO₃, Kalkwasser, Sodium hydroxide, anything?

I'm pretty sure a few of my corals would die pretty fast when phosphate rises and falls 0.6ppm every 24 hours...

 

[AlexandraDreadlocksPanda]

I don’t believe those results are feasible for one minute. ..

 

[AlexandraDreadlocksPanda]

This still feels like an absolute stretch as a difference of 0.6ppm is absolutely insane, but are you dosing anything that might cause phosphate precipitation or a pH change? CaCO₃, Kalkwasser, Sodium hydroxide, anything?

I'm pretty sure a few of my corals would die pretty fast when phosphate rises and falls 0.6ppm every 24 hours...

Absolutely. Even with what you suggested with Kalk precipitating PO4, I think it comes back to your statement that corals would die pretty fast with that sort of catastrophic chemistry going on…

 

[Ziggy17]

I don’t believe those results are feasible for one minute. ..

Yes, I’m lying. Lol

 

[Dan_P]

Last feed time is 2 hours prior to evening test to eliminate that issue. I’m stumped as well.

If you can, it would be helpful to make phosphate measurements throughout the day to determine what the trend in PO4 concentration looks like between the two readings. I assume/hope you don’t work 7 days a week. :-)

 

[Boehmtown]

You fed during the day. Some of the stays as particulates which makes the test read high. They've been processed by the morning. I'd trust the morning reading as your real phosphate. To test. Don't feed one day and do the tests. Only other thing I could think, is ambient light if it's a Hannah

 

[EnterName]

Do you guys think a faulty test kit might be a possibility?

What if in reality there only is a rather small phosphate change between day and night (e.g. 0.05ppm) but the test kit amplifies the readings by some factor. This would explain why results are repeatable but corals are fine with the change and it is not causing any issues.

 

[BriDroid]

Mine will fluctuate throughout the day, but mine is always less in the middle of the day and more in the morning. I do dose Plus-NP in 4 doses between 9am and 2pm. I also dose Phos-Feed at 10:30pm, after dark. I’ll take a reading in the morning, usually around 0.08-0.1ppm. If I take it in the afternoon, it will be 0.03-0.04ppm. I’m guessing it’s the Phos-Feed being used up as things are growing? These are taken with the Hanna ULR Phosphorus checker.

 

[Malum Argenteum]

The phosphate test results can be pushed high by suspended particles.

As I understand the operation of the Hannah checker (I use one), this inaccuracy would be eliminated by zeroing the meter on the pre-reagent water. That's the purpose of the 'C1' phase of the test procedure.

 

[Ziggy17]

The corals are not fine.
Torches are retracted, Goni reracting, zoas not happy, a stylo is starting to bleach out a bit.
That’s why I posted to look to stabilize before i start losing them.

 

[EnterName]

Mine will fluctuate throughout the day, but mine is always less in the middle of the day and more in the morning. I do dose Plus-NP in 4 doses between 9am and 2pm. I also dose Phos-Feed at 10:30pm, after dark. I’ll take a reading in the morning, usually around 0.08-0.1ppm. If I take it in the afternoon, it will be 0.03-0.04ppm. I’m guessing it’s the Phos-Feed being used up as things are growing?

I think a change of 0.06 is realistic and can be attributed to phosphate consumption and precipitation.

But OP has 10 times as much, so the test kit must be off or so.

 

[Ziggy17]

I think a change of 0.06 is realistic and can be attributed to phosphate consumption and precipitation.

But OP has 10 times as much, so the test kit must be off or so.

What causes a Hanna to be off? As mentioned, I changed out the battery.

Do they have a shelf life and require replacement after a certain amount of tests? If so, I’m happy to buy a new one.

 

[EnterName]

I think a change of 0.06 is realistic and can be attributed to phosphate consumption and precipitation.

But OP has 10 times as much, so the test kit must be off or so.

What causes a Hanna to be off? As mentioned, I changed out the battery.

A bad reagent is the only thing I can think of, that could explain why the results are repeatable.

Scratches/dirt on the vial or a broken LED/photosensor would not produce repeatable results. Do you have access to a different test kit? It would be interesting to see if another test kit would show the same results.

Very high alkalinity can also mess with some phosphate tests (Salifert for example has a warning that it won't operate properly at 20dKH).
The hanna alkalinity reagent goes bad relatively fast and shows too low alkalinity levels. If you adjusted alkalinity according to these readings you might have elevated alkalinity too far and now it's messing with the phosphate readings. (You see I'm trying to check every single possibility that comes to my mind even if it is unlikely).

 

[Malum Argenteum]

A bad reagent is the only thing I can think of, that could explain why the results are repeatable.

Scratches/dirt on the vial or a broken LED/photosensor would not produce repeatable results

Neither of those would explain the consistent daily pattern, though.

 

[EnterName]

A bad reagent is the only thing I can think of, that could explain why the results are repeatable.

Scratches/dirt on the vial or a broken LED/photosensor would not produce repeatable results

Neither of those would explain the consistent daily pattern, though.

A bad reagent or photosensor that amplifies a small change that occurs during the day by a factor x would explain the consistency.

If alkalinity messes with the test and is dosed between the tests it would also explain consistency. But I fully agree that all these are unlikely factors.

 

[Ziggy17]

Alk is sitting around 8.3. Reagents are a month old. Vial is brand new as I just bought new ones a couple weeks ago as the indicator line was mostly gone on three of my vials. Has to be particulate. Only thing that explains the consistent results. Which means my corals prefer PO4 over .1