Alkalinity Dosing Calculator

How the sums work

Raising 1 litre by 1 dKH takes 1 ÷ 2.8 = 0.357 milliequivalents of alkalinity. Baking soda supplies 1 milliequivalent per 84 mg. Soda ash supplies 1 milliequivalent per 53 mg, because each carbonate counts twice. So soda ash raises alkalinity further per gram.

For a liquid product, the calculator uses the dose on its label instead: so many ml raises so many litres by so much dKH.

How fast is safe?

Bulk Reef Supply suggests raising alkalinity by no more than 1.4 dKH a day and watching that pH doesn’t move more than 0.2. The calculator starts at 1 dKH a day to give a margin. You can change it, but going faster rarely helps.

Once you’re at target, work out your tank’s daily use and switch to a small daily maintenance dose. See why alkalinity drops for how.

Baking soda or soda ash?

Both raise alkalinity. Baking soda (sodium bicarbonate) slightly lowers pH as it goes in. Soda ash (sodium carbonate) raises pH. Bulk Reef Supply notes this difference. Soda ash is often preferred in tanks where pH runs low; baking soda is gentler where pH is already high.

You can make soda ash from baking soda by baking it in an oven, which drives off water and carbon dioxide. Use plain sodium bicarbonate, not baking powder, which contains other ingredients.

Dosing it safely

Weigh it on scales rather than using spoons. Dissolve it fully in RODI water, then add it slowly to a high-flow area such as the sump, away from corals. Bulk Reef Supply says it is much safer to dose less and test again than to overdose.

Test the next day before adding the next part. If the rise is more or less than expected, check your tank volume first. Our tank volume calculator helps.

How much baking soda raises 1 dKH?

About 3.0 g per 100 litres.

Can I add it all at once?

Only if the rise is small. Split anything over about 1 dKH across days.

Will it affect calcium?

Not directly. But high alkalinity with high calcium can cause precipitation, so test both.