Not understanding phosphate consumption

[Reefen]

I am dosing Nitrates and Phosphates both nutrients where 0 from vodka dosing. what I am seeing is that the phosphate is being used a lot and not the nitrates. is this normal?

 

[rkpetersen]

Phosphorus is incorporated at approximately 1/16 the rate that nitrogen is. (Actual ratio varies considerably.)
So for every 1 ppm of nitrate incorporated into algae, about 0.06 ppm phosphate should be used.
Also, both have to be available. If either is limiting, the other will build up.

 

[Reefen]

so, if I am understanding correctly what is happening in my tank does not make sense. my nitrate is staying at 2.5 I have not added any nitrate. but if I put in enough phosphate to get a reading of .043 it is 0 the next day

 

[Tombones]

Its my understanding from Randy and other experienced reefers that when you take your PO4 down to 0 it is also taken out of the live rock and when you add PO4 back to the tank the live rock takes it up quickly. Keep adding PO4 until you get a constant desired reading. I also used GFO and had the same problem and now I add PO4 weekly to maintain a desired reading. I hope this helps.

 

[PatW]

I dose both nitrates and phosphates. Nitrates stay at 2 or 3 ppm. I keep phosphates at.03 ppm but they bounce around. If they run a bit low, I think that anything that wants phosphate grabs it running the levels down to 0. If there is more than enough phosphate, the levels can go up.

 

[Dan_P]

I am dosing Nitrates and Phosphates both nutrients where 0 from vodka dosing. what I am seeing is that the phosphate is being used a lot and not the nitrates. is this normal?

Nitrate is not the only nitrogen source in an aquarium. It just happens to be the one we can measure and the one that can accumulate. Phosphate is still needed.

I saw the response suggesting that the aragonite sand and rocks are adsorbing PO4. You can easily determine if this is happening. Use a small reagent spoon to measure out a small quantity of rinsed aquarium sand. Use about 0.1-0.2 mL. Just swirl the sand with aquarium water to clean it. If the aquarium water is really reading zero PO4, add a volume to the sand that is big enough for a PO4 test. Cap the container and let it stand in the dark 2 days. Test the water in the container. If the sand has really been stripped of phosphate, you will measure zero PO4. If the PO4 measurement is greater than zero, the sand still has phosphate adsorbed and is being consumed faster than it can accumulate in the water.

 

[Reefen]

just want to thank everyone for the replies, all have been helpful, I am starting to see the phosphate use level off. I am also now in the process of switching over to chaeto in a refugium. I am giving the refugium another go after having no luck, but there are alot of things I understand better now.

 

[Randy Holmes-Farley Verified Community Expert]

It is a fact that when trying to raise phosphate, a huge amount will bind to calcium carbonate surfaces.

When trying to lower phosphate, it comes back off.

in a sense, the rock strongly buffers the phosphate level to stay the same, despite efforts to raise or lower it.