Confused by phosphate readings - need advice

[emilese]

I have a new Hanna phosphate checker HI713. The first time I used it (about 2 weeks ago), I got a reading 0.00. But, when I took it yesterday, I first got a reading of 0.18. I thought I did something wrong, so I took it again, and the 2nd time it read 0.2.

Part of me thinks my Hanna checker is not producing correct readings as I do not feed heavy (once a day, pellets or frozen), I run a skimmer, and I have a low bioload (only a Royal Gramma, 2 cleaner shrimp, a few crabs, a cowrie, lps, sps, and a couple softies).

The other part of me wonders if it is indeed correct as I have been battling cyano. But, the cyano has been receding. I was planning on running some phosguard in filter bag for a few days but, if the cyano is receding without it, I don't want to change things (I think the weekly 10% water changes have helped)

The only thing that I can think of that my have caused the phosphate reading to shoot up is that I haven't seen one of my snails in a while and a small hermit crab may have died as I haven't seen it move in a few days.

Need some advice, should I add the PhosGuard since the readings were so high? Could the Hanna checker be off?

Here are my other parameters:
Salinity: 1.026
Temp: 79
PH: 8.1
Alk: 7.4
Calcium: 475
Mag: 1360

Thanks.

[ramseynb]

.17 and .2 are pretty close readings. It’s not going to be exact every time. Unfortunately, our hobby test kits are good at fixing a close estimate, but aren’t super precise scientific instruments. If you’re really worried, buy an ICP or similar test and get a lab test done. I’d probably run some GFO or other phosphate reducing substance but I’d go very slow. It also would depend on the coral I was keeping. For SPS, yeah, I’d want it lower. For LPS and softies,’it’s probably nothing to worry about. My phos has been about .1 for some time and I’m trying to get it lower but only because my tank will be SPS dominant. I already have quite a few LPS frags and they’re doing great. Great color and growing fast for LPS.

[emilese]

Originally Posted by ramseynb

.17 and .2 are pretty close readings. It’s not going to be exact every time. Unfortunately, our hobby test kits are good at fixing a close estimate, but aren’t super precise scientific instruments. If you’re really worried, buy an ICP or similar test and get a lab test done. I’d probably run some GFO or other phosphate reducing substance but I’d go very slow. It also would depend on the coral I was keeping. For SPS, yeah, I’d want it lower. For LPS and softies,’it’s probably nothing to worry about. My phos has been about .1 for some time and I’m trying to get it lower but only because my tank will be SPS dominant. I already have quite a few LPS frags and they’re doing great. Great color and growing fast for LPS.

Thanks for the reply. I'm not concerned about the difference between the two readings of .18 and .2. What concerns me is the difference from 0.00 to .18 (or .2). I'm wondering if my Hanna checker is off or what could have caused it to spike so much given that I don't overfeed (at least I think) and I have a low bioload. I'm also a little confused because the cyano that I have been dealing with is receding even with that high of a phosphate reading. I seems like if that number were correct, the cyano shouldn't be receding. All of the corals are healthy, growing, with good color

[RobZilla04]

Likely the resulting 0.00 reading was due to the cyano using up available phos thereby none is left in the water to display a test result. Now that it is receding you're seeing either the true value of the phos or the cyano die off is increasing the level.

Either way .2 is not terrible. You'll find many SPS tanks that run higher than NSW level. Just monitor and keep it in check along with cyano & algae.

[Dan_P]

The zero reading was likely not zero but something above zero. Your system did not jump from 0 to 0.2. Also, 0.2 ppm is really more like 0.15 to 0.25 ppm.

If you had repeated the test when you saw zero, the next test or two would probably not have been 0 ppm. That is just how analytical measurements work. This "noise" in the Hanna Checkers is normal and expected.

I would interpret your measurements as your system had an increase PO4 concentration of 0.1 - 0.2 ppm over a week period. So what does that mean?

In absolute terms, the PO4 concentration change is significant enough to take notice and maybe start monitoring the PO4 concentration more often to determine if this is a continuing trend or a temporary spike. If you have been trending your data already, that is a good start in answering the question "so what?" to the increase.

I wouldn't conflate the cyanobacteria growth and the phosphate concentration. Treat them as two different trends for now because bulk water chemistry tests while useful do not correlate well to nuisance organism growth. In your case, the bulk water PO4 level was zero and you had cyanobacteria growth already.

[ClownNut]

Bioload is not about how many fish/invert you have, it's how much food you put into your tank.
if your tank consumes + export nutrient > or = than the input nutrient(from feeding or if you dont use RO/DI water) you will have low/zero nutrient. if not, you will have nutrient buildup over time.
the Hanna is giving you the correct result. the meter has +/- 0.03. you are well within that range.

[nereefpat]

I think you want the ultra low-range (ULR) hanna checker, if you want to be picky.

[emilese]

Originally Posted by RobZilla04

Likely the resulting 0.00 reading was due to the cyano using up available phos thereby none is left in the water to display a test result. Now that it is receding you're seeing either the true value of the phos or the cyano die off is increasing the level.

Either way .2 is not terrible. You'll find many SPS tanks that run higher than NSW level. Just monitor and keep it in check along with cyano & algae.

This makes a lot of sense. I thought high phosphates = cyano. So, my confusion was if the cyano is receding, my phosphates should be lowering not rising.

[emilese]

Originally Posted by Dan_P

The zero reading was likely not zero but something above zero. Your system did not jump from 0 to 0.2. Also, 0.2 ppm is really more like 0.15 to 0.25 ppm.

If you had repeated the test when you saw zero, the next test or two would probably not have been 0 ppm. That is just how analytical measurements work. This "noise" in the Hanna Checkers is normal and expected.

I would interpret your measurements as your system had an increase PO4 concentration of 0.1 - 0.2 ppm over a week period. So what does that mean?

In absolute terms, the PO4 concentration change is significant enough to take notice and maybe start monitoring the PO4 concentration more often to determine if this is a continuing trend or a temporary spike. If you have been trending your data already, that is a good start in answering the question "so what?" to the increase.

I wouldn't conflate the cyanobacteria growth and the phosphate concentration. Treat them as two different trends for now because bulk water chemistry tests while useful do not correlate well to nuisance organism growth. In your case, the bulk water PO4 level was zero and you had cyanobacteria growth already.

Thanks Dan_P, I will keep monitoring.

[RobZilla04]

I may be mistaken but I thought cyano tends to form when phos get close to or higher than nitrate.

[emilese]

Originally Posted by ClownNut

Bioload is not about how many fish/invert you have, it's how much food you put into your tank.
if your tank consumes + export nutrient > or = than the input nutrient(from feeding or if you dont use RO/DI water) you will have low/zero nutrient. if not, you will have nutrient buildup over time.
the Hanna is giving you the correct result. the meter has +/- 0.03. you are well within that range.

Good point about bioload. Yes, I have an RO/DI unit and I've been using since Day 1.

[emilese]

Originally Posted by nereefpat

I think you want the ultra low-range (ULR) hanna checker, if you want to be picky.

Yeah I wanted the ULR checker but, I made a mistake when I ordered it.

[bertoni]

Phosphate and cyanobacterial blooms don't necessarily correlate well. It's possible to have a zero measured phosphate level and lots of cyanobacteria and, on the other hand, for the phosphate level to be high with no cyanobacteria. If the cyanobacteria is receding, the phosphate level would rise if there were constant input of phosphate and no new consumer stepping up to the plate. Reducing lighting is a very common way to get into this zone.

[LobsterOfJustice]

I just started using the checker a few months ago and in my experience it took a while before I started getting readings that made sense. I think a lot of it is user error or at least getting a few tests under your belt so that you perform the test in a consistent way every time. I also switched to only using one of the vials for all my tests, just to remove that as an additional variable. I started performing all my tests in duplicate like you mentioned and did that for several weeks until I was confident that I was receiving accurate results.


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