Contradictory phosphate tests

Randy Holmes-Farley · Jun 9, 2021

Cunning_plan said:
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?

I doubt it.

Koigula · Dec 23, 2021

Cunning_plan said:
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?

On the same subject, you will also get different results using the Hanna Phosphate ULR above and the Hanna Phosphorous. Here is a descriptive video showing 0.03 with method above and 56 ppm = (56*3.066 /1000) = 0.18 ppm by the phosphorous method. To add to confusion the video conversion is wrong.

What do you do as a hobbyist then? I tend to use Sailfert and ignore the rest