The relationship between Nitrates and Phosphates

[taurus19]

Hi everyone, my first thread so go easy on me! Now to provide a bit of context to the problem, I have a mixed reed and I know everyone says not to chase numbers - which I agree with. But if your tanks a few years old you can easily have PO4 at around 0.40ppm and Nitrates around 40ppm or even higher and everything will be looking great- until you introduce a new coral like some Gonis - which simply wont open under those conditions (new Corals vs exiting ones). Now, I am trying to reduce my Nitrates which are around 32ppm and P04 around 0.13 ppm. I do want to bring my Nitrates back down to around 15-20ppm. The problem is any liquid dosers (for example the NYOS nitrate removal) also actually affect the phosphates. So, if my nitrates go down it will also bring down my phospahtes with them. Can anyone elaborate on the realtionship between these two? i.e. reducing Phospahte -> also reduced Nitrates. reducing NItrates-> reduces phospahates and so on. I dont think i really understand this relationship and I would really like to ! Also, is it actually possible to reduce nitrates without touching phopshates ??
Thanks for your help

 

[Randy Holmes-Farley]

Organic carbon dosing is unlikely to have much impact on phosphate for at least two reasons (denitrification and a big reservoir of phosphate bound to rock and sand)

Water changes will also drop nitrate and have not much impact on phosphate for the same rock binding reason.

 

[taurus19]

Sorry I meant this one not NYOS:

Quantum LR Nitrate Remover, is this also same as carbon dosing?​

 

[Randy Holmes-Farley]

Sorry I meant this one not NYOS:

Quantum LR Nitrate Remover, is this also same as carbon dosing?​

Yes, it is.

 

[taurus19]

Sorry adding more to this for someone that wants more info - I ran an experiment with the whole carbons dosing and this is what I found:
1. If your nitrates are high e.g. 20ppm as you carbon dose the bacteria will reduce your nitrate but will also reduce your phosphates. I could see a drop from 0.20ppm to 0.10ppm on phosphates over 2 weeks with no other reactors/ Rowaphos.
2. Reason is as the bacteria population consumes your Nitrates it will also consume phosphates but at a much smaller rate. So, when your nitrates are high, your phosphates will reduce but will slow down as your Nitrate levels drop. E.g. Nitrates at 10 ppm with carbon dosing may not reduce your phosphates that effectively. and if your nitrates are close to 0, it will have no effect at all on your phosphates as there is nothing to feed the bacteria. So Nitrate is the limiting factor.

In essence over long term Carbon Dosing is effective with Nitrate but not phospahtes.

I hope the "why" is clear as I saw it and if anyone would like elaborate that would be appreciated.

 

[Randy Holmes-Farley]

I hope the "why" is clear as I saw it and if anyone would like elaborate that would be appreciated.

I would add that another reason is that the process of denitrification driven by organic dosing consumes nitrate but not any phosphate:

organic + 124 NO3– + 124 H+ → 122 CO2 + 70 N2 + 208 H2O