Nitrate and phosphate issue

CiterSquash

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Hello all, been feeding for a while, I have high phosphates and bottomed out nitrates, I’ve tried GFO, phoseguard and no matter what I do, the phosphates always come back up and the nitrates stay bottomed out. Any help would be great!


 

exnisstech

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What are your test results? What is often considered high PO4 really isn't high at all it just gets repeated very often that low PO4 is needed and that has not be true IME. I find dosing ammonium works very well to raise NO3. I dose PO4 when I test 0 and will run small amounts if GFO if my Hanna ULR PO4 tester is flashing 0.9

EDIT: I can't explain the science but often increasing NO3 can help to lower PO4. Randy has a good article on dosing ammonium for low NO3 tanks.

 
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CiterSquash

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What are your test results? What is often considered high PO4 really isn't high at all it just gets repeated very often that low PO4 is needed and that has not be true IME. I find dosing ammonium works very well to raise NO3. I dose PO4 when I test 0 and will run small amounts if GFO if my Hanna ULR PO4 tester is flashing 0.9

EDIT: I can't explain the science but often increasing NO3 can help to lower PO4. Randy has a good article on dosing ammonium for low NO3 tanks.

20260209_120819_CEEB1FA5-505D-4FFC-9545-0976BEB88E9F.png
 
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CiterSquash

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What are your test results? What is often considered high PO4 really isn't high at all it just gets repeated very often that low PO4 is needed and that has not be true IME. I find dosing ammonium works very well to raise NO3. I dose PO4 when I test 0 and will run small amounts if GFO if my Hanna ULR PO4 tester is flashing 0.9

EDIT: I can't explain the science but often increasing NO3 can help to lower PO4. Randy has a good article on dosing ammonium for low NO3 tanks.

My pho is just about .2 and my No is 0
 

exnisstech

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Personally I would ignore PO4 and try to bring up NO3 a little then keep an eye on things. Many will say PO4 of 0.2 is high but I don't find that to be the case.
No high end acro or anything but this tank has always run high PO4 and has been over 0.9 at times. I will run some GFO when it's that high but mostly because it's the max my tester can measure and I do like to have idea where they're are.

Last test NO3 was 15 and PO4 0.45
PXL_20251108_012602277~2.jpg
 

Mr. Mojo Rising

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If you are using the API phosphate tester then throw it out. That tester shows range from 0 to .25, then the next range is from .25 to .5. My phosphate is at .03, API just can;t test it, its not accurate enough.

Honestly I would not make any changes to the tank based on API tests, even the nitrate is just a guide but not accurate enough to start messing with tank chemistry. Upgrade the test kits before doing anything else IMO, good luck
 

Randy Holmes-Farley

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I agree that the phosphate is fine, and I'd look to get N up by feeding more or dosing N in some fashion.


4. What targets seem reasonable? Of course, that depends on all the other factors at play, such as types of corals, availability of ammonia, particulate foods, etc. However, for a mature mixed reef, this would be how I personally would run it:
  • Let nitrate float between 5 ppm and 50 ppm. I’d use gentle export in this range, such as growing macroalgae.
  • Above 50 ppm, I’d begin to focus more on reducing it, by organic carbon dosing, turf or macroalgae, etc.
  • Below 5 ppm, I’d begin to dose ammonia or feed more. The target level might drop lower if dosing ammonia, just like the heavy in/heavy out scenario where nitrate may not be as needed.
  • Let phosphate float between about 0.06 ppm and 0.3 ppm. This range is higher than I’ve recommended in the past. I’d use gentle export in this range, such as growing macroalgae.
  • Above about 0.3 ppm, I’d begin to focus more on reducing it, by turf or macroalgae, or a binder such as GFO or lanthanum (has its own risks to tangs). If a binder: GO SLOW. Turf and macroalgae will typically be slow enough.
  • Below 0.06 ppm, I’d begin to dose sodium phosphate or feed more to get the level up.
 

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