Nopox and low ph

[Peer.Boerner]

I have a 50 net gallon mixed reef, primarily LPS with a few simple SPS (Montipora, Pocillopora, stylophora) and all is going well. I was managing phosphate with gfo but believe (perhaps incorrectly) that using diy nopox would be better due to the increased bacteria as a food source for the coral. Over 8 weeks I’ve slowly increased the dose from 0.5 ml to 2.5ml. All is going well but I’ve noticed my ph has gone from its low of 8.1 at night to 7.9. These values are fine, but I’m wondering why has it dropped? The diy nopox vinegar relative to the overall water volume is very small.

Here are my tank parameters:
Alk 8.5
Ca: 440
Mg: 1380
Phos: 0.12
Nitrate: 14.5
Salinity: 1.026
Temp: 77.5 to 78.5
Alk, phos and nitrate measured with Hanna checkers.
Ca and Mg with Salifert

I’m going to continue the dosing because all looks well. This is more of a curiosity question.
appreciate any insights you can share.

 

[exnisstech]

House closed up because it's getting colder outside?

 

[Peer.Boerner]

House closed up because it's getting colder outside?

Yes but I’ve connected my skimmer to an out door air line (1/2” pvc) and co2 scrubber. This has been in place prior to the nopox. But even here in Florida we’re a little more closed up than normal.

 

[Randy Holmes-Farley Verified Community Expert]

yes, NOPOX lowers pH, and it is not just the vinegar. All ingredients in it (such as ethanol) end up as CO2, lowering pH.

FWIW, while vinegar has more up front pH lowering, vodka has more later and the net effect on pH is the same.

 

[Peer.Boerner]

yes, NOPOX lowers pH, and it is not just the vinegar. All ingredients in it (such as ethanol) end up as CO2, lowering pH.

FWIW, while vinegar has more up front pH lowering, vodka has more later and the net effect on pH is the same.

Many thanks! Didn’t realize the vodka played a role.

 

[EnterName]

yes, NOPOX lowers pH, and it is not just the vinegar. All ingredients in it (such as ethanol) end up as CO2, lowering pH.

FWIW, while vinegar has more up front pH lowering, vodka has more later and the net effect on pH is the same.

Do you happen to remember any reasonable source for the net reactions that takes place to convert the carbon source to CO₂?

Google spits out a few, but they are either combustion reactions or don't have a proper source:

Vinegar: CH₃COOH + HCO₃⁻ → CH₃COO⁻ + CO₂ + H₂O
Acetate: CH₃COO⁻ + 2 O₂ → HCO₃⁻ + CO₂ + H₂O
Ethanol: C₂H₆O + 3 O₂ → 2 CO₂ + 3 H₂O
Sugar: C₁₂H₂₂O₁₁ + 12 O₂ → 12 CO₂ + 11 H₂O​

I guess you know why I'm looking for those

 

[Randy Holmes-Farley Verified Community Expert]

Those look fine. Add the first two together and the HCO3- and acetate cancel out to give

CH₃COOH + 2O2 → 2CO₂ + 2H₂O