pH and Alkalinity Consumption

[ajnies]

Hello all!

I'm curious about the relationship between pH and alkalinity consumption in my tank. I understand that a higher pH promotes faster growth as well as both biotic and abiotic precipitation, but I'm wondering how much of an increase in alkalinity consumption I should expect when raising my pH from 7.95 to 8.05.

This relatively minor increase in pH has had a drastic effect on my alkalinity consumption. Typically I dose around 40ml per day or soda ash, after raising the pH, I was needing to dose around 70 ml of soda ash to maintain my alkalinity at 8.5. My tank is around 45 gallons and is lightly stocked with mostly lps.

Does this increase seem realistic? Over the past couple months I've toyed with raising the pH several times and the result has always been the same. However, it just feels like a very drastic increase in the amount of dosing required for a relatively small pH increase.

 

[blaxsun]

From my own arguably limited experience, chasing those higher pH numbers almost always come at a higher associated cost - be it more dosing or running a Co2 scrubber.

 

[ajnies]

From my own arguably limited experience, chasing those higher pH numbers almost always come at a higher associated cost - be it more dosing or running a Co2 scrubber.

Thanks. I'm definitely not trying to chase numbers. My main goal was simply a stable pH somewhere around 8, but if that means doubling the alk dosage for a low stocked tank, it's probably not worth it.

 

[Randy Holmes-Farley]

It's not really possible to state in a general way how much alk demand increase there is as pH increases.

Assuming you are using my recipe for the soda ash (such as BRS uses), then 70 mL in 45 gallons is about 2.2 dKh per day. That is not especially high, particularly if you also have good coralline growth, but it is worth watching to see that you have not initiated excessive precipitation of calcium carbonate on pumps, heaters, or in a sand bed (it hardens up). Once that starts it is self feeding to drive more (positive feedback loop of fresh crystal surfaces actign to seed more precipitation).