High Phosphate, Happy with Nitrate

[ZaphodBB]

Looking for help bringing Phosphate down without bringing Nitrate down.
Nitrate 10 ppm
Phosphate 0.45 ppm

This is down from a high of (as of Nov 2025, slowly brought down since then):
Nitrate >50PPM
Phosphate > 1.57 PPM

That high was after over correcting raising nutrients after a dino bloom last year from zero'd out nutrients. Dino's successfully eliminated (uv sweeper did the trick).
I'm happy with Nitrate at 10ppm, but would like to cut phosphate atleast in half (preferably more, target of ~0.1ppm phosphate).

Problem is feeding more heavily seems to raise phosphates more than nitrate.

What I'm doing now is dosing Ammonium Chloride to bring nitrates up. The thought is to input more nitrate via dosing rather than foods alone which would add both Nitrate and Phosphate. Then as organism uptake nitrate and phospate, the ratio should slowley drop into the range I'm looking for.

Am I on the right track?

I'd like to avoid GFO, because I'm worried about stripping Phosphate.

Tank details.
A year and a half old.
90 gal
Nitrate 10 ppm
Phosphate 0.45 ppm
ALK 7.4 - Got this dialed in. Doesn't swing.
Specific Gravity 1.024
Temp ~78F
Dosing 7.5ML of AFR solution a day via auto doser.
Monthly 20% water changes.

Filtration:
No sump/skimmer.
Tunze Algae reactor for nutrient control and filter floss in a Tunze commeline for mechanical filtration.

Stocking:
Moderately stocked with fish/inverts (~10 fish, with juvenile Kole Tang being the largest).
Moderate coral load.
Softies (zoas/mushrooms/gorgonians) and SPS(Montis/anacropora/ birdnests/Letpo)corals happy. LPS (Duncan/Frogspawn/Acan's) less than happy, aside from the Letpa corals which are very happy.

 

[tmcca]

I use Blue Life Phosphate RX. Use only half of recommended dosage. Google search a calculator. Some fish very sensitive though with phosphate rx so caution. Also, gradually lower phosphates and see corals and fish reaction. I have never had a problem using phosphate rx but there is a caution.

 

[bobnicaragua]

I mix Carbon and GFO in a filter bag and throw it in the sump. It’s much more gentle than running a reactor. Just start with a table spoon or two of GFO and see where your phosphates are after a month.

 

[Randy Holmes-Farley]

I'm not certain you will see any benefit from lowering phosphate, but assuming you want to, the options include:

1. GFO (you can use as little as you want, so there's no concern going to far)
2. A balanced export method such as growing macroalgae, coupled with adding nitrate or ammonia (I do this one)
1. Lanthanum (you can use as little as you want, so there's no concern going to far, but there is a tang risk)

 

[ZaphodBB]

Thanks for the replies everyone.

I wouldn't care to much except the LPS's aren't happy. And the phosphates the only thing I see that's off on parameters.

It's weird as torches/Duncan's/frogspawn were happy and growing new heads prior to the Dino outbreak. Post dinos everything else is happy, but not the LPSs. So clearly something's different now than before.

I'll continue with option 2 Randy. As I'm currently growing chaeto as the primary export, and upped my ammonia dosing as of yesterday. I'll continue this for a few weeks, and if no change perhaps I'll try option 1 or 2. Thinking a small amount of GFO in the tunze filter.

 

[ReefGeezer]

When I has phosphate issues, I used Tropic Marin ElimiPhos Rapid (Lanthanum Chloride product). It works well... over time... and didn't bother my Tangs.

 

[CHSUB]

I would double your percentage of wc to 10% weekly, not necessarily critical important, more my preference for optimization, during WC I would focus on detritus removal and blowing with a turkey baster. I would not worry about no3 and po4 going lower and much lower is perfect, imo! Corals and fish tanks do best when pollution is at a minimum. Dinos and general nuisance organisms do not bloom in clean environments. A little GFO is not going to strip po4 and might help lower po4 further with increased maintenance. I would discontinue dosing; and feed fish and corals directly.