PO4 fluctuations

[Necrodaemus]

Are there any risks to corals (SPS specifically) with fluctuations in PO4? Mine seems to run between 0.1 and 0.04. I test daily, usually around the same time each day and I see it go up and down like this. I do not run any phosphate binding media….just a skimmer (running very dry) and a small amount of chaeto in a small 5g-ish section in my sump on a reverse light cycle (11p to 10a).

 

[EeyoreIsMySpiritAnimal]

That fluctuation should not be a problem, but your sps corals will tell you if 0.1 is too high.
(It's not too high for most tanks, but some SPS are more picky and need a true ULNS)
The thing to watch for is a trend of levels climbing over days/weeks, and to make sure they don't bottom out.

 

[Randy Holmes-Farley]

I doubt this any concern, and I wonder how much is real variation and how much is testing variability.

 

[Necrodaemus]

I doubt this any concern, and I wonder how much is real variation and how much is testing variability.

My thoughts exactly. I test with a Hanna ULR that measure ppb which is said to have an accuracy of +/-5ppb which definitely could be mean the difference of +/-0.015ppm. This puts my mind at ease.