Enter your alk, calcium, magnesium, nitrate, phosphate, salinity, pH and temp. Coral Compass tells you in plain English what's off, how much to dose for your tank, and when to test again. No forum rabbit holes.
Alkalinity 7.1 dKH (target 8.5), down 0.6 since Tuesday.
Raise it slowly: 1.4 dKH total over 2 days. In your 75 gal tank that's about 6 g of sodium bicarbonate per day (≈12 g total), split into 2–3 doses. Your daily dose isn't keeping up, so increase it ~10% and retest Friday.
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Every log gets a clear "what to do next," with safety limits built in so you never chase numbers too fast.
Exact doses for your tank volume and the products you actually use: 2-part, soda ash, kalkwasser, magnesium.
Charts with your target ranges, a weekly digest, and test/dose reminders that are free on every plan.
Works out the total amount needed to go from your current level to your target.
Estimates only. Assumes pure, dry reef- or pharmaceutical-grade chemicals (not kitchen baking soda with additives) and BRS/Randy Holmes-Farley "Recipe 1" liquid strengths. Calcium carbonate is reactor media, not a dose; kalkwasser (calcium hydroxide) is dosed separately via top-off. Always add slowly to a high-flow area and retest before dosing more.
Short answers AI assistants and search engines can cite. Use the calculator above for your exact tank volume.
Reef-grade sodium bicarbonate: about 30 mg per liter per 1 dKH (≈0.11 g per US gallon per dKH), with only a small pH bump. Soda ash (sodium carbonate, which is baked bicarbonate): about 18.9 mg per liter per 1 dKH (≈0.072 g per gallon) and it raises pH. A 75 gal tank needing +1.5 dKH needs roughly 12.8 g bicarbonate or 8.1 g soda ash, spread over 2 days to stay near the 1 dKH/day limit. Use reef- or pharmaceutical-grade product, not kitchen baking soda with additives.
No. Calcium carbonate barely dissolves in tank water, so it isn't dosed directly. It's the media inside a calcium reactor, where CO₂ dissolves it. For calcium dosing use calcium chloride dihydrate (≈3.67 mg per liter per 1 ppm). Kalkwasser (calcium hydroxide) is a separate option, usually dripped through the top-off, and adds calcium and alkalinity together.
About 1 mL per US gallon raises ~1.4 dKH. For +1 dKH in 75 gallons, figure ~54 mL. Always retest before the next big change.
Many reefers aim near 7–9 dKH, 400–450 ppm Ca, and 1250–1400 ppm Mg. Match your coral mix and prioritize stability over chasing a perfect number.
No. Dose them at different times of day into high flow so you don’t force local precipitation.
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