Does Red Sea KH actually raise pH?

jasonrusso · Dec 31, 2017

Whenever I add the Red Sea B KH liquid additive, the pH quickly spikes but then goes back to where it was before after a little while. My KH was about 9.1 and I want it at 11. So I added 20ml to my RSM 130 (half a dose because Red Sea says no more than 1.4dKH at a time). This made the pH go from 8.05 to 8.35. After about 2 hours it will be close to where it started. None of the corals seem affected, none of the fish seem to mind either. Is the pH actually that high or is it a false reading?

cmcoker · Dec 31, 2017

It is probably the actual pH. Plain baking soda would raise the alk without so much of a pH bump. Kalkwasser would send it higher than what you are seeing. It's probably sodium carbonate (soda ash) primarily in your additive, so a moderate bump that goes down after a while is normal.
If you could split that into a few doses over the day would probably be better, so the pH doesn't spike so much at once

rkpetersen · Dec 31, 2017

Also, if you're using a pH probe, where is your probe in relation to where you're dosing? You may be capturing a pH spike (in the sump, for example) that doesn't actually reflect global conditions in the tank.

jasonrusso · Dec 31, 2017

This is an AIO RSM 130. The probe is in the sump chamber but on the other side of the tank.

rkpetersen · Dec 31, 2017

The pH and ORP probes on the other side of my sump from the 2-part dosing tubes and the skimmer/ozone outlet show larger and more acute changes in response to dosing, as compared to matching probes positioned in the overflow. Sometimes there will be a fairly dramatic change on a sump probe and virtually no record of it on an overflow probe. Of course every set up is different.

jasonrusso · Dec 31, 2017

rkpetersen said:
The pH and ORP probes on the other side of my sump from the 2-part dosing tubes and the skimmer/ozone outlet show larger and more acute changes in response to dosing, as compared to matching probes positioned in the overflow. Sometimes there will be a fairly dramatic change on a sump probe and virtually no record of it on an overflow probe. Of course every set up is different.

I don't think that you read that the spike lasts for a couple hours. This is more than enough time for the buffer to dissipate into the water.

Randy Holmes-Farley · Dec 31, 2017

jasonrusso said:
Whenever I add the Red Sea B KH liquid additive, the pH quickly spikes but then goes back to where it was before after a little while. My KH was about 9.1 and I want it at 11. So I added 20ml to my RSM 130 (half a dose because Red Sea says no more than 1.4dKH at a time). This made the pH go from 8.05 to 8.35. After about 2 hours it will be close to where it started. None of the corals seem affected, none of the fish seem to mind either. Is the pH actually that high or is it a false reading?

A high pH additive (carbonate or hydroxide) will cause a temporary deficit in CO2 in the water relative to the air and cause the pH to rise. The tank then continues to pull in CO2 from the air and the pH drifts back toward where it started.