Contradictory phosphate tests

[Cunning_plan]

I'm having a bit of a conundrum with my phosphate tests. For the past year I have been using the red sea test kit, whilst not particularly easy to read I have felt comfortable that my levels have been stable at the 0.12 level. I recently bought a Hanna checker to try and help get more precision, the number was off the charts..

Red sea

Hanna (90% diluted with rodi)

I completed the Hanna test 3 times at normal concentrations and 1 time at a 90% dilution. I read the instructions as nauseum and validated that the reagent was marked the same as the checker.

The tank is 180 gallons with a mid sized though affective refugium running along with a skimmer. Nitrates are stable at 5 ppm. Has been up for 3 months and contains about 2/3 new dry rock.

I do not currently have access to a shop to help test my water.

In general the corals in my tank look great, really nice colours though almost no growth. I had put that down to oddities in my alk which has been very slowly rising since I set the tank up... 2dkh in 3 months.

Does anyone have any thoughts? My assumption is the red sea test being the most likely?

 

[elorablue]

I'm beginning to think that our hobby test kits give nothing more than 'ballpark' results.
I have the regular range Hanna phosphate checker and the other day did a test and got 0.00. Decided to double check and then not 15 minutes later got a 0.04.
Colour matching, counting drops, using the exact amount of reagent etc etc. it all just begs for inaccuracies.
And don't get me started on the Salifert Calcium and Magnesium test kits!

 

[Cunning_plan]

If you look at the photo the solution is almost entirely clear yet it reads as 0.5... is that expected behaviour for this colorimeter?

 

[fachatga]

I’ve had this same problem. I think what happens is your phosphates are off the chart for the redsea test so you can’t rely on it. The Hanna is correct. And yes it will seem pretty clear even tho it’s high. At least that’s my guess.

 

[PatW]

If you look at the photo the solution is almost entirely clear yet it reads as 0.5... is that expected behaviour for this colorimeter?

I use the Hanna ULR phosphorous detector so slightly different. If I can see any color whatsoever, that means the phosphate levels are really high.

 

[Cunning_plan]

I use the Hanna ULR phosphorous detector so slightly different. If I can see any color whatsoever, that means the phosphate levels are really high.

Thanks, that's helpful. When I didn't dilute it it was navy blue closing on black which is a little terrifying!

 

[Dan_P]

I'm having a bit of a conundrum with my phosphate tests. For the past year I have been using the red sea test kit, whilst not particularly easy to read I have felt comfortable that my levels have been stable at the 0.12 level. I recently bought a Hanna checker to try and help get more precision, the number was off the charts..

Red sea

Hanna (90% diluted with rodi)

I completed the Hanna test 3 times at normal concentrations and 1 time at a 90% dilution. I read the instructions as nauseum and validated that the reagent was marked the same as the checker.

The tank is 180 gallons with a mid sized though affective refugium running along with a skimmer. Nitrates are stable at 5 ppm. Has been up for 3 months and contains about 2/3 new dry rock.

I do not currently have access to a shop to help test my water.

In general the corals in my tank look great, really nice colours though almost no growth. I had put that down to oddities in my alk which has been very slowly rising since I set the tank up... 2dkh in 3 months.

Does anyone have any thoughts? My assumption is the red sea test being the most likely?

Hanna tests are the most accurate of the hobby tests and the company tells you how accurate it is. No other company will tell you this information. You have no idea how well they perform. Also, all tests except Hanna rely on your ability to judge color intensity. So, Hanna is the test to trust.

As for the Red Sea results, the color of test solution is green not blue as seen on the color wheel. I would suspect something is up with the Red Sea kit.

 

[Cunning_plan]

Yes, it has always looked to be a lot greener than the colour wheel. The wheel itself never really worked for me to be honest. I just assumed that was a 'feature' of the test.

I'm sending off an icp test tommorow but am also adding some gfo now. Will keep an eye on both tests in the interim.

 

[Dan_P]

Yes, it has always looked to be a lot greener than the colour wheel. The wheel itself never really worked for me to be honest. I just assumed that was a 'feature' of the test.

I'm sending off an icp test tommorow but am also adding some gfo now. Will keep an eye on both tests in the interim.

The ICP will very likely give you phosphorous results lower results than actually exist in your system.

 

[Calm Blue Ocean]

I’ve had this same problem. I think what happens is your phosphates are off the chart for the redsea test so you can’t rely on it. The Hanna is correct. And yes it will seem pretty clear even tho it’s high. At least that’s my guess.

I wonder if this is the problem because I also have this issue. And in every case where the Hanna and Red Sea disagree, the number that the Hanna is giving me is significantly higher than the Red Sea test kit range. My Hanna results have typically been pretty close to ICP test numbers.

 

[Cunning_plan]

Joy. This because of the bound phosphate?

 

[Calm Blue Ocean]

Joy. This because of the bound phosphate?

Hopefully someone can answer. I'm currently at war with phosphate in my tank to the point that there is clearly something I'm not understanding. I sure wish the Red Sea test was correct because then I wouldn't be having heart failure right now.

 

[blasterman]

Why i stick to the salifert. Its not the most precise, but it only reads three states; no phosphate, about .03 to. 05 which is just right, or too darn high.

 

[Shirak]

If you look at the photo the solution is almost entirely clear yet it reads as 0.5... is that expected behaviour for this colorimeter?

I use the ULR Phosphate checker also. Looks about right color wise for the reading it's showing. I have done enough now to just look at the vial and get a rough estimate on the PO4. Not sure if that is good or bad or just shows I have done entirely too many phosphate tests..

 

[ru4serious]

I have the hanna ulr HI736 and I trust it, phosphate was at zero, I added the loud wolf trisodium phosphate, in increments according to the James planted tank calculator. After a few days dosing to get a measurable amount, the hanna followed the doses almost exactly

 

[Koigula]

I use the Hanna ULR Phosphorus checker.

I find this test needs much more care to get a good result than other hobby grade tests. I triple rinse the test vial with RODI water in a squeeze bottle. Everyone should really have a few squueze bottles to run tests. Once the vial is rinsed I wipe with a micro cloth. After that for remainder of test only top and bottom of vial should be touched. Rewiping vial will alter results. I cut packet on dotted line and peal apart packet flat to a rectangle and fold in half. Do not touch the foil liner either.I can get repeatable results this way and poor repeatability with touching wiping the foild or vial surface. Using a medical 10 cc syringe may help a bit too. I usually fill from a dedicated sampling cup. This test is one that I run a few times.

Aside from that I only feed seawead and fronzen foods. Pellets are for neighbors if I am out of town. Testing needs go down with time as it becomes more stable.

 

[Koigula]

I'm having a bit of a conundrum with my phosphate tests. For the past year I have been using the red sea test kit, whilst not particularly easy to read I have felt comfortable that my levels have been stable at the 0.12 level. I recently bought a Hanna checker to try and help get more precision, the number was off the charts..

Red sea

Hanna (90% diluted with rodi)

I completed the Hanna test 3 times at normal concentrations and 1 time at a 90% dilution. I read the instructions as nauseum and validated that the reagent was marked the same as the checker.

The tank is 180 gallons with a mid sized though affective refugium running along with a skimmer. Nitrates are stable at 5 ppm. Has been up for 3 months and contains about 2/3 new dry rock.

I do not currently have access to a shop to help test my water.

In general the corals in my tank look great, really nice colours though almost no growth. I had put that down to oddities in my alk which has been very slowly rising since I set the tank up... 2dkh in 3 months.

Does anyone have any thoughts? My assumption is the red sea test being the most likely?

That is a strong blue tint and likely more correct than you want it to be.

You will also see the same thing going from Nyos Nitrate Test kit to a Hanna ULR Nitrate test kit. In my case the Nyos subjectice 2-5 ppm reads at 12 ppm Nitrate with Hanna ULR kit.

Even with high tests I make slow adjustments to the tank. Stripping it all with GFO is not good. In used 4 tablespoons per 250 gallons of GFO put through a very slow trickle to reduce phosphate over 2 -3 months and then discontinued GFO use. GFO discharge can be measured too with a 30% single pass reduction in my case.

 

[Randy Holmes-Farley Verified Community Expert]

Joy. This because of the bound phosphate?

By "This" you mean what?

ICP may be lower than rapid tank measurements due to the possibility of phosphate consumed by microorganisms in transit.

 

[Cunning_plan]

ICP may be lower than rapid tank measurements due to the possibility of phosphate consumed by microorganisms in transit.

That's both a simpler and more fascinating answer than I was expecting,

Does that mean I'd be more likely to get a more comparable result by testing from the outflow of my UV in both cases?

 

[ChaosAquaculture]

I'm having a bit of a conundrum with my phosphate tests. For the past year I have been using the red sea test kit, whilst not particularly easy to read I have felt comfortable that my levels have been stable at the 0.12 level. I recently bought a Hanna checker to try and help get more precision, the number was off the charts..

Red sea

Hanna (90% diluted with rodi)

I completed the Hanna test 3 times at normal concentrations and 1 time at a 90% dilution. I read the instructions as nauseum and validated that the reagent was marked the same as the checker.

The tank is 180 gallons with a mid sized though affective refugium running along with a skimmer. Nitrates are stable at 5 ppm. Has been up for 3 months and contains about 2/3 new dry rock.

I do not currently have access to a shop to help test my water.

In general the corals in my tank look great, really nice colours though almost no growth. I had put that down to oddities in my alk which has been very slowly rising since I set the tank up... 2dkh in 3 months.

Does anyone have any thoughts? My assumption is the red sea test being the most likely?

In my personal experience, I’ve had more fluctuations with Hana than Red Sea. Besides the fact that you have been basing your tanks parameters off of Red Sea this far. For a simpler, and also relatively accurate reading I’d recommend salifert.