pH Drop when adding Alk

[Jeremy King]

I have been seeing an odd behavior when I add alkalinity to my system. The pH instantly drops 0.1 when I add it, and it takes 3 to 4 hours to come back up to normal. I've been using the Red Sea Reef Care Program (Foundation A/B/C, Trace Elements A/B/C/D, and Coral Nutrition A/B). Now, I thought adding part B (the alkalinity/carbonate part) would increase the pH, not make it spike not drop? Am I misunderstanding something about how dosing affects water parameters, or is something odd going on?

Last measurements from this weekend, in case it's needed: pH 7.95-8.1, Ca 475, Alk 8.1, Mg 1300, salt 34.5-35, temp ~77.5-79

 

[glb]

I have been seeing an odd behavior when I add alkalinity to my system. The pH instantly drops 0.1 when I add it, and it takes 3 to 4 hours to come back up to normal. I've been using the Red Sea Reef Care Program (Foundation A/B/C, Trace Elements A/B/C/D, and Coral Nutrition A/B). Now, I thought adding part B (the alkalinity/carbonate part) would increase the pH, not make it spike not drop? Am I misunderstanding something about how dosing affects water parameters, or is something odd going on?

Last measurements from this weekend, in case it's needed: pH 7.95-8.1, Ca 475, Alk 8.1, Mg 1300, salt 34.5-35, temp ~77.5-79

That's strange. My ph usually goes up when I dose alk. Following to see if someone can explain it.

 

[zachxlutz]

How are you measuring pH? Probe? How much of are you adding? There are two types of alkalinity solutions, one will raise pH while the other will decrease pH. I'm not sure what the Red Sea formulation is.

 

[Jeremy King]

I'm measuring with the Apex pH probe. I'm adding from 30-70g into a 180g tank.

I take RO/DI water (about a 1 pint), measure in the Foundation B powder, and mix it up. Wait 5-10 for it to dissolve, and then pour it into the tank, 2-5 ounces at at time, over 3-5 min. If I put in too much powder for it all to dissolve into the water, I pour most of the water into the tank, then full it up with more water, mix it up some more so the rest will dissolve.

 

[zachxlutz]

Hmmmm... Sounds like the right method. Maybe someone like @Randy Holmes-Farley could help answer?

 

[Randy Holmes-Farley Verified Community Expert]

I don't know what they put into their alkalinity supplement, but such products can be formulated to provide a range of effects from a small pH drop (using bicarbonate only) to no effect (a mix of mostly bicarbonate and some carbonate, the exact ratio depends on the pH at which you do not want it to change) to a substantial pH boost (using only carbonate). :)