Phosphate Fluctuations?

atp0726 · Jan 25, 2019

This week I received my ATI ICP results. Right before sending out the sample I checked my Phosphate with Hanna ULR and it was .04, right where I try and keep it. ICP showed it was actually at .01. I think the acceptable scale is +/- .03 so ok with that. It did get me thinking though I may want to assume the Hanna is reading low and keep PO4 a bit higher.

I currently dose nitrate and try and manage po4 via feeding. I actually use flake in the morning because i feel like it adds a bit more p04 and feed LRS reef frenzy in the evening fairly generously. A few times a week before bed i feed BRS reef chili.

I normally test in the evening about a half hour after feeding the LRS frozen and my po4 on Tuesday this week was .09. On a whim i just checked it this am before feeding the flake and it was only at .02. Which according to my recent ICP that could mean its 0.

Should I be concerned about po4 fluctuating between feedings and maybe try dosing p04 rather than trying to mange through feedings? Maybe feed a bit more food? My nitrate remains stable and i only need to dose once or twice a week in order to keep it around 5-10.

Tank is over 2 years old and just started adding SPS frags to it a few months ago and in the process of adding more. I am getting good color, growth could maybe be a bit better. Frags are only around 2 mths old however. Alk remains steady at 7.9

RobZilla04 · Jan 25, 2019

ATI ICP also showed my Po4 lower than what my Hannah Phosphorus ULR tests reveal. I've left it alone and do nothing different. The ICP tests all have their own margin of error and shouldn't be treated as 100% gospel IMO.

Gareth elliott · Jan 25, 2019

I think the po4 and no3 results they provide like their alkalinity measurement are done with lab grade titration tests. The icp test only will tell the overall phosphorus number which for all intent and purposes is not useful to the hobbyist. As such agree above there is going to be an error range, but might be wider than their pure element icp portion of the results. Your not showing zero and not above .1 i would change nothing with a
.01 result.

atp0726 · Jan 25, 2019

RobZilla04 said:
ATI ICP also showed my Po4 lower than what my Hannah Phosphorus ULR tests reveal. I've left it alone and do nothing different. The ICP tests all have their own margin of error and shouldn't be treated as 100% gospel IMO.

Gareth elliott said:
I think the po4 and no3 results they provide like their alkalinity measurement are done with lab grade titration tests. The icp test only will tell the overall phosphorus number which for all intent and purposes is not useful to the hobbyist. As such agree above there is going to be an error range, but might be wider than their pure element icp portion of the results. Your not showing zero and not above .1 i would change nothing with a
.01 result.

Both good points. It was the only test that differed from the numbers i was getting with my test kits so probably got put under the microscope.

I am thinking the best time to measure po4 is not right after the tank is fed heavily and maybe do it before. That should give me a better baseline what the po4 is running at in between feedings.