Does feeding affect nutrient testing

[ScottD]

The other day I tested for nitrate and phosphate and found my tank was running a little higher than it normally is. I wasn’t surprised since it had been a little while since I last tested and I’ve added a couple fish and increased my feeding since the last test. But I also had the realization that I tested shortly after I fed them. It made me wonder does feeding recently affect test results?

 

[KrisReef]

Yes it can.

 

[rogueshrimp88]

I've always assumed so. Usually on my test day I collect samples first at roughly the same time in the morning before feeding. Then I feed and test the the "untainted" samples.

 

[DanyL]

I try to always test in roughly the same hour, and also to fit in a window of 6 to 8 hours after last feeding or any nutrient related change (such as dosing NH4 for example).

This provides me with reliable results in an “idle” system, meaning without any external influence/spikes (or rather more normalized test conditions).

 

[BryanM]

If you test after feeding you're likely going to see higher nitrate and phosphate numbers.

 

[Garf]

It made me wonder does feeding recently affect test results?

If folk are saying it does, then I'm not sure of the mechanism considering the test kits only pick up the inorganic portions. I've tested foods and sand bed crud with both tests before and nothing has ever shown up.

 

[Dan_P]

The other day I tested for nitrate and phosphate and found my tank was running a little higher than it normally is. I wasn’t surprised since it had been a little while since I last tested and I’ve added a couple fish and increased my feeding since the last test. But I also had the realization that I tested shortly after I fed them. It made me wonder does feeding recently affect test results?

Maybe phosphates might be affected, nitrates no.

 

[DanyL]

If folk are saying it does, then I'm not sure of the mechanism considering the test kits only pick up the inorganic portions. I've tested foods and sand bed crud with both tests before and nothing has ever shown up.

I personally had consistency issues with my test results, mainly testing PO4 with the Hanna checker, which makes sense because even the slightest contamination makes it unreliable from my experience. I assume it’s more due to water clarity (not something you would notice with the naked eye though), since it’s a colorimeter.

The reason for the 6 to 8 hour window is simply because once I need to wait for the water to be clear again, the food starts to break down and than actually influence the water chemistry, and a determined time frame normalizes the results between tests.

 

[Pod_01]

I always assumed it does, but I never did check. Good question…

 

[Reeferbadness]

Also cleaning your glass of algae can add to nutrient level.... i also always test around the same time (about an hour before 4pm feeding) and make sure to not fiddle with the tank for a few hours before.... god forbid i get a high Phos reading LOL