my pH is 8.2, but Alk is low

reefmaster70 · Mar 18, 2026

Hey all.

I have a question about raising my Alk level. I just tested my tank today, my pH is 8.2 and my Alk is only 6.7 Now I know that's not super low, but I like it to be up around 8.3 or so. I have been dosing both AFR and Kalkwasser in the evenings, as i've always had horribly low pH, even with a calcium reactor attached to the skimmer air intake.

So I am dosing 10ml of AFR over about 4 hours at night and then Kalkwasser I am dosing 14ml from about 6pm-midnight. My tank is 75g mixed reef with 20g sump.

I am just wondering if I should up the dosage of AFR or Kalk to bring the Alkalinity up, or not worry about it?

Thanks

CoralBiomorph · Mar 18, 2026

AFR is meant to maintain alkalinity. Not to raise it. I would dose a small bit of dissolved baking powder in RODI water to raise my alkalinity.

reefmaster70 · Mar 18, 2026

CoralBiomorph said:
AFR is meant to maintain alkalinity. Not to raise it. I would dose a small bit of dissolved baking powder in RODI water to raise my alkalinity.

why not just kalkwasser?

exnisstech · Mar 18, 2026

I use AFR but not kalk. I use AFR to make small increases in my alk levels. I know the directions say to use it to maintain vs increase but I only did that when I started using AFR about 2 years ago. Consumption increases and alk drops I just increase my AFR. Just have to wait a couple of days to test since it takes a while to release.

I target 8.5 dkH but I'm good with anything 8-9

CoralBiomorph · Mar 18, 2026

flyweed said:
why not just kalkwasser?

Because it also raises your calcium.

Randy Holmes-Farley · Mar 18, 2026

Use the kalk, and add way, way more. 14 mL in that size tank is close to nothing. You might need a half gallon or more
Per day.

It’s fine to keep using AFR as well, but it tends to lower pH while kalk raises it.

I’d at least use 500 mL of kalk per day and see what that does.