Nopox drove down my phosphates to undetectable?

[ScottB]

Can I ask a possibly dumb question? How do you dose phosphates? I had something terrible in my 300 gallon tank and the only thing that helped save the day was NOpox. I’ve been running it for a few months now, should I stop? Phosphates read zero but tank looks great?

If you are measuring PO4 with a Hanna Ultra Low checker and getting zero you may be playing with fire. Dinoflagellates will bloom and corals will perish.

You may be safe if you are feeding the fish A LOT OF FISH FOOD. I have seen it work in rare instances, with big tanks, and feeding 8 times per day.

"How" to dose PO4 has many possibilities. In an emergency, dosing bottled phosphate solutions is common as @John Hernandez listed. Brightwell also has NeoPhos. The there are also many DIY solutions that may be more economical at your volume. I use this:

 

[Randy Holmes-Farley Verified Community Expert]

Sounds right.. but what happens if i keeping dosing phosphate... NO3 will keep coming down even if i am not using nopox? eventually nitrate will be gone? or since i am not dosing nopox that won't happen?

Foods keep adding nitrate. Might it get too low? Possibly, but not because of residual organics leftover in the water. I don't think that happens.

 

[4sylvester]

Yeh.. i confirmed over several days a reading of zero on my hanna ULR meter so i decided to dose phosphate. I am a chemist so i calculated exactly how much Sodium Phosphate (NaH2PO4) to add. Made a convenient concentrated solution and 5mL of my solution added to the display raises Phosphate 0.05 ppm. BINGO! worked like a charm with amazing accuracy. So... as many of you predicted that phosphate would deplete quickly. You were right. I am having to dose 0.05 ppm twice a day to keep it detectable on the Hanna ULR. My nitrates were still at 20. So is it safe to assume that with phosphates being consumed so readily that Nitrates should be coming down?

 

[ScottB]

Yeh.. i confirmed over several days a reading of zero on my hanna ULR meter so i decided to dose phosphate. I am a chemist so i calculated exactly how much Sodium Phosphate (NaH2PO4) to add. Made a convenient concentrated solution and 5mL of my solution added to the display raises Phosphate 0.05 ppm. BINGO! worked like a charm with amazing accuracy. So... as many of you predicted that phosphate would deplete quickly. You were right. I am having to dose 0.05 ppm twice a day to keep it detectable on the Hanna ULR. My nitrates were still at 20. So is it safe to assume that with phosphates being consumed so readily that Nitrates should be coming down?

Assuming you have rock & substrate, much of the initial PO4 is being stored rather than depleted. So for a while it will be hard to keep PO4 in the water at least until the rock saturates. Then you will need less & less.

As to nitrate depletion, some folks here have suggested a causal relationship (when PO4 goes up then NO3 will fall) but I have not personally witnessed that. The reverse is certainly true in my experience. Like clockwork.

 

[Randy Holmes-Farley Verified Community Expert]

So is it safe to assume that with phosphates being consumed so readily that Nitrates should be coming down?

As noted above, the phosphate isn’t all or perhaps not even mostly being used by organisms. A lot will be binding to rock and sand surfaces.