Dosing Nitrate to Lower Phosphate

[SoCalVictor]

Hello,

I have historically struggled to keep phosphate below 0.15ppm (Hanna) even running HC GFO through a reactor. My nitrate usually measures around 1ppm (Salifert).

A few days ago, my phosphate was measuring 0.22ppm and my glass had algae, which is usually my indication to change out my GFO. For whatever reason, my HC GFO only lasts about a 7 days. I've been running GFO for about 5 months now and prior, my phosphate was very high, above the Hanna threshold. I had slowly brought it down using GFO. My hope is that my rock and substrate have released most of the bound phosphate but I can't be certain.

This time I tried to dose (on 2/15) a small amount of nitrate, using Seachem's Flourish Nitrogen product and did not change out the GFO. Tonight (about 36 hours later) I measured my GFO, and it's at 0.1ppm. Nitrate is still at 1ppm.

Am I correct to assume that the nitrate dosing brought down the Phosphate level?

thanks in advance,
Victor

 

[Lasse]

For me - this indicate a nitrogen depleted tank. When adding NO3 - you promote some growth (corals, algae or other organisms that use photosynthesis) 1 ppm with salifert can be 0 nitrate if your nitrite hit 0.02 mg/L. IMO a rather common concentration in established tanks.

Wait some days and see whats happen.

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

You are also measuring phosphate days later than the first measurement. Many folks find ups and downs of phosphate if they measure multiple times a day, so it might be an N deficiency that you reduced with the dosing, or it might just be random variation and/or test error (whatever is driving the variable results that others report in a single day)..

 

[SoCalVictor]

Measured this morning. Phosphate at 0.14 and Nitrate reads about the same, 1ppm.

PE on my SPS are much more pronounced than I've ever seen.

 

[Randy Holmes-Farley Verified Community Expert]

Many folks find that dosing nitrate is desirable. IMO, food grade sodium nitrate is a good source.

 

[SoCalVictor]

Phosphates jumped back to 0.21 on Friday. Measured again on Sunday and it was still around there at 0.22.

Kinda bummed that dosing the nitrate did not have a permanent effect on the phosphate.

 

[mdb_talon]

Phosphates jumped back to 0.21 on Friday. Measured again on Sunday and it was still around there at 0.22.

Kinda bummed that dosing the nitrate did not have a permanent effect on the phosphate.

Did you dose additional nitrate in that time and what is nitrate at now? If the system truly was limited by N then it may have used up what you dosed and again limited by N again.

 

[Randy Holmes-Farley Verified Community Expert]

Phosphates jumped back to 0.21 on Friday. Measured again on Sunday and it was still around there at 0.22.

Kinda bummed that dosing the nitrate did not have a permanent effect on the phosphate.

I'm not sure that any effect you saw wasn't just test error, but the flux of phosphate into and out of a reef aqaurium is on the order of 0.05 to 0.2 ppm daily, so anything that alters that flux needs to keep doing it if you want an ongoing effect.

 

[SoCalVictor]

Nitrate was at 2ppm on Friday and I dosed nitrate again. I did not test Nitrate on Sunday but did test the phosphate.

My phosphate previous to the nitrate dosing did not have big swings so I was guessing/hoping that the nitrate dosing was the differentiator here.