Low PO4 Higher NO3

gdemos · Apr 6, 2015

My tank is 100% SPS and Heavy Fishload, Heavy Feeding, Biopellet, Live Rock
I have always used the Hanna Ultralow Phosphorous meter showing 14-23 Phosphorous ppb (call it .06 Phosphate).
Yet my recent Triton results showed .016 mg/l (so I'm going with this)

Meanwhile, Salifert NO3 tests 5-10ppm (i struggle with the color chart so i have my not so color blind wife read it for me).

I am not terribly concerned with Nitrate at 10ppm generally speaking.

My question is: is it technically possible to have this 'elevated' NO3 meanwhile such a low PO4?

The research I have done seem to have no perfect correlation between NO3 and PO4 other than the general, one can limit the other, if one is low the other is also low.

I'm dialing back my Biopellet effluent as a result of the Triton P 5.26 ug/l and PO4 .016mg/l findings...and beginning to believe my Salifert is off.
I also have a Pinpoint NO3-N monitor, which in the rare occasion that I can get it calibrated, I see 10-13 NO3N which would suggest something in the neighborhood of 40+ppm NO3.
Maybe Salifert is off, maybe Pinpoint is off, not sure.

Appreciate your thoughts.
-Greg

shred5 · Apr 6, 2015

Well I have had nothing but problems with salifert test kits and hobby test kits are not exactly accurate to begin with.. Something like hach would be better.
Also test kits only read one type of phosphates. Basically your phosphate maybe higher than you think.

With carbon dosing you need all 3: nitrate, carbon and phosphate and if phosphate gets low carbon dosing at that point is useless. Normally carbon is the limiting factor that is why people add it. ,I guess it is possible at some point one of the others become limiting and phosphate is your limiting factor now and at this point carbon and nitrate rise.

gdemos · Apr 6, 2015

As I have read the 'redfield ratio' does not apply in our reefs.
I have also read that the export "ratio" is impossible to know.
Also unlikely to know, but surmised that certain tank inhabitants uptake NO3 and PO4 in varying or unknown proportions.

So is it safe to say in relative terms that if Triton readings show .016 PO4, that my Salifert NO3 is likely incorrect at 10ppm +/- and I likely have Lower NO3 than Salifert is telling me?

Triton does not test HCP NO3 in the US, so kind of stuck it seems with hobbyist kits, and I am not inclined to believe my Pinpoint NO3 meter as noted in OP.

Well, i'm continuing my heavy/diverse feeding and tuning down my Biopellet reactor despite the Salifert test I guess...just going based on Triton's PO4 being really low.

Randy Holmes-Farley · Apr 6, 2015

Depending on the imports and exports, yes it is certainly possible to have low nitrate and high phospahte or high phospahte and low nitrate. Both can easily be found among reefers.

As to which of multiple test methods might be more accurate, that is very hard to really say.