How much does baking soda raise KH?

Roughly 1 gram of pure sodium bicarbonate per US gallon raises alkalinity by about 1.4 dKH. The tool scales this to your tank volume and the dKH gap, so you can dose precisely instead of guessing.

What is the difference between dKH and ppm?

dKH is German degrees of carbonate hardness; ppm expresses the same thing as milligrams of calcium carbonate per litre. They convert directly: 1 dKH equals 17.86 ppm CaCO3. Pick whichever unit your test kit reports.

Should I dose all at once?

No. Raise KH by no more than about 1 dKH per day in a stocked tank to avoid shocking fish and corals. If the calculated dose is large, split it across several days and re-test between doses.

Why does KH keep dropping?

Biological processes, coral and plant calcification, and CO2 injection all consume carbonates over time. A stable KH needs regular dosing or a buffered water-change routine rather than a single correction.

Can I use commercial buffer instead of baking soda?

Yes. Commercial KH buffers are sodium bicarbonate or carbonate blends sold at a stated potency. Enter your product's grams-per-dKH-per-volume rating and the tool gives the equivalent commercial dose alongside the baking-soda figure.

Aquarium Alkalinity (KH) & Buffer Calculator

Carbonate hardness (KH) is the buffering capacity that keeps aquarium pH stable. When KH drops, pH becomes unstable and can crash. This calculator tells you exactly how much sodium bicarbonate (plain baking soda) or commercial buffer to add to raise KH from where it is now to your target.

How it works

The dose is based on a well-established hobby rule: about 1 gram of pure sodium bicarbonate per US gallon raises alkalinity by ~1.4 dKH. Rearranged for any volume and any KH gap:

gap (dKH)   = target KH − current KH
grams NaHCO3 = (gap / 1.4) × (volume in US gallons)

Volumes entered in litres are converted at 3.785 litres per US gallon first. If your test kit reads in ppm CaCO3, divide by 17.86 to get dKH before entering.

Tips and example

A 200 litre (about 52.8 US gallon) reef tank at 6 dKH that you want at 8 dKH has a 2 dKH gap, needing roughly (2 / 1.4) × 52.8 ≈ 75 g of baking soda. Raise no faster than ~1 dKH per day in a stocked system, so split that into two doses on separate days and re-test in between. Always dissolve the powder in a cup of tank water and add it slowly to a high-flow area rather than dumping it dry.