How to maintain phosphates

Porcupine Reefer · Dec 12, 2025

I had a massive dinoflagellate outbreak in the past few months, and took the necessary steps to fight it off. I dosed PNS pro bio's purple non sulfuric bacteria, dosing 150 ml daily until I killed the bottle. Fed my cope pods reef nutrition's phyto feast and they've exploded in population ever since, and finally dosed bright well's Neo phos and Neo nitro. My tank has now been looking way better than it has been months, but I am recently running into a problem. I dosed Neo nitro until I got 5 ppm in nitrates and wanted to keep my phosphate at .25 ppm, but I'm struggling to keep that level of phosphate stable. While my nitrate has been stable for a few weeks now, my phosphate has gone up and down, and it recently went down fast. Just yesterday on Dec 11 my phosphate read at .25 ppm, and just today on Dec 12 it read zero. I tested my water with the fritz test kits, and they gave me consistent results. I feed my tank once every two days in order to keep nutrients down, but it's only my nitrate that stays stable. I know that my protein skimmer is extremely efficient and I did adjust it, but what else could be keeping the phosphate down? the hair algae plummeted after I pulled it out and got my nitrate at 5 ppm, and so did the dino's. The dino's are still in my tank only not as bad, is it because i'm not feeding enough? my only concern with that is my nitrate would spike, what's the best course of action?

Subsea · Dec 12, 2025

Porcupine Reefer said:
I had a massive dinoflagellate outbreak in the past few months, and took the necessary steps to fight it off. I dosed PNS pro bio's purple non sulfuric bacteria, dosing 150 ml daily until I killed the bottle. Fed my cope pods reef nutrition's phyto feast and they've exploded in population ever since, and finally dosed bright well's Neo phos and Neo nitro. My tank has now been looking way better than it has been months, but I am recently running into a problem. I dosed Neo nitro until I got 5 ppm in nitrates and wanted to keep my phosphate at .25 ppm, but I'm struggling to keep that level of phosphate stable. While my nitrate has been stable for a few weeks now, my phosphate has gone up and down, and it recently went down fast. Just yesterday on Dec 11 my phosphate read at .25 ppm, and just today on Dec 12 it read zero. I tested my water with the fritz test kits, and they gave me consistent results. I feed my tank once every two days in order to keep nutrients down, but it's only my nitrate that stays stable. I know that my protein skimmer is extremely efficient and I did adjust it, but what else could be keeping the phosphate down? the hair algae plummeted after I pulled it out and got my nitrate at 5 ppm, and so did the dino's. The dino's are still in my tank only not as bad, is it because i'm not feeding enough? my only concern with that is my nitrate would spike, what's the best course of action?

‘I know that my protein skimmer is extremely efficient and I did adjust it, but what else could be keeping the phosphate down?‘

If you are dosing nitrate & phosphate and still have low numbers, considering your efficient protein skimmer, then consider returning skimmate to tank. I consider 5ppm of nitrate low.

joeyhatch11 · Dec 12, 2025

While dosing anything phosphate related to boost your levels, nitrates will always drop. Take a moment and Google it as I did and it'll all make sense. I'm currently going through this myself. Nitrates were 14.5 but started dosing trisodium phosphates by Loud Wolf to raise my phosphates that were reading zero and my nitrates dropped to 11.5. I'm finding myself upping my sodium nitrate dosing to combat my phosphate dosing. Understand that by dosing phosphates they will bind to the rock and sand in a tank but at some point, through continued dosing, it will level out and stabilize. You need to test and keep testing to detect this change.

joeyhatch11 · Dec 12, 2025

Subsea said:
‘I know that my protein skimmer is extremely efficient and I did adjust it, but what else could be keeping the phosphate down?‘

If you are dosing nitrate & phosphate and still have low numbers, considering your efficient protein skimmer, then consider returning skimmate to tank. I consider 5ppm of nitrate low.

Or another option is to dial it back and skim dry vs wet if thats the case.

Subsea · Dec 12, 2025

joeyhatch11 said:
While dosing anything phosphate related to boost your levels, nitrates will always drop. Take a moment and Google it as I did and it'll all make sense. I'm currently going through this myself. Nitrates were 14.5 but started dosing trisodium phosphates by Loud Wolf to raise my phosphates that were reading zero and my nitrates dropped to 11.5. I'm finding myself upping my sodium nitrate dosing to combat my phosphate dosing. Understand that by dosing phosphates they will bind to the rock and sand in a tank but at some point, through continued dosing, it will level out and stabilize. You need to test and keep testing to detect this change.

Joey,
Phosphate getting sequestered into mineral formation is one sink for phosphate. Consider that all photosynthetic organisms require both N & P, so your coral and algae will uptake inorganic minerals with N:P:K as the majors.

When I sent Red Ogo, Gracilaria Parvispora, to a regional agriculture lab, analysis showed the N:P ratio to be 30:1. With some fast growing Caulerpa’s the ratio is 100;1.

The ratio of N:P in micro algae (phytoplankton) is 16:1 which in Oceanography is the Redfield Ratio.