Kalk dosing with Co2 scrubber And Alk Rapidly Decreasing

Millz034 · Mar 8, 2022

I started Dosing kalk about 4 months ago because of low ph. The kalk wasn't really raising ph but it raised my alkalinity to 10 Dkh After doing some research I got a co2 scrubber. My ph went from 7.9 with 7.7 lows to 8.3 with 8.2 lows. The only thing is now my alkalinity drops almost .5 daily. over 3 weeks it is at 7.7. I want to start dosing Alkalinity but i am not sure what the best way to dose it would be there are many ways but I am not sure with dosing it with kalk. My tank is only a 20 gallon with a 10 gallon sump. It is filled with lps. I wouldn't have started dosing but over the 2 years it has been running everything has been growing very slowly. When i raised my ph the corals had a growth spurt and filling out the tank better.
Any suggestions on Alkalinity supplement and should I drop the kalk and just dose alk an calcium i also manually dose magnesium because the kalk lowers it.

20 gallon with 10 gallon sump
Salinity 1.025
calcium 435
magnesium 1300-1350
alk 7.7 and not raising
PH 8.2-8.3

Spare time · Mar 8, 2022

You could add soda ash or bicarb (depending on your pH) or just try bicarb and calcium alone without kalk.

Reefahholic · Mar 9, 2022

Why not just increase the Kalk dose? That’s a small tank. The Kalk can easily handle the demand for a while.

Randy Holmes-Farley · Mar 9, 2022

Demand for alk and calcium will rise as the pH rises, so it is normal to need more now.

Any sort of normal alk and calcium dosing method is fine, including more limewater/kalkwasser, a two part, etc.

arking_mark · Mar 9, 2022

Measure tank daily demand over a week
Choose ionically balanced dosing products
Use reef calculator for daily dosing and limit individual dosing to no more than 0.25dKH

nereefpat · Mar 9, 2022

+1 for using kalk. It sounds like you are already set up for it. 0.5 dKH per day can be easily be dosed with kalk. If usage starts to get to 1-2+ dKH per day, it's a little more difficult to meet the demand with kalk.

reddogf5 · Mar 9, 2022

Randy Holmes-Farley said:
Demand for alk and calcium will rise as the pH rises, so it is normal to need more now.

Any sort of normal alk and calcium dosing method is fine, including more limewater/kalkwasser, a two part, etc.

Why does higher pH increase the demand for calcium and alkalinity Randy?

Randy Holmes-Farley · Mar 9, 2022

reddogf5 said:
Why does higher pH increase the demand for calcium and alkalinity Randy?

Two reasons.

1. Abiotic precipitation of calcium carbonate increases as pH increases. The tendency to precipitate is directly driven by the multiplication product of the calcium concentration times the carbonate concentration. The biggest driver is pH (higher pH drives bicarbonate to carbonate). A difference of 0.3 pH units (say, 7.9 to 8.2) is a factor of 2 in carbonate. A difference of 0.6 pH units (7.8 to 8.4) is a difference of about a factor of 4 in carbonate concentration.

2. Some (many? all? ) hard corals calcify faster at higher pH. Whether that is because there is more carbonate around to take up to make calcium carbonate, or because they take up bicarbonate and have to spit out the H+ to make carbonate is not perfectly clear:

HCO3- (bicarbonate --> CO3-- (carbonate) + H+

In any case, spitting out H+ into the water is easier when there is less of it in the water pushing back, and pH is a direct measure of the amount of H+ in the water.

reddogf5 · Mar 9, 2022

Randy Holmes-Farley said:
Two reasons.

1. Abiotic precipitation of calcium carbonate increases as pH increases. The tendency to precipitate is directly driven by the multiplication product of the calcium concentration times the carbonate concentration. The biggest driver is pH (higher pH drives bicarbonate to carbonate). A difference of 0.3 pH units (say, 7.9 to 8.2) is a factor of 2 in carbonate. A difference of 0.6 pH units (7.8 to 8.4) is a difference of about a factor of 4 in carbonate concentration.

2. Some (many? all? ) hard corals calcify faster at higher pH. Whether that is because there is more carbonate around to take up to make calcium carbonate, or because they take up bicarbonate and have to spit out the H+ to make carbonate is not perfectly clear:

HCO3- (bicarbonate --> CO3-- (carbonate) + H+

In any case, spitting out H+ into the water is easier when there is less of it in the water pushing back, and pH is a direct measure of the amount of H+ in the water.

Thanks! Do you happen to have an article that discusses #1?