Daily consumption calculator
Once corals grow, alkalinity and calcium fall every day. Two tests a few days apart tell you how much your tank uses, and so how much to dose each day to hold it steady.
Formulas and sources last checked . How we check
Calculator
Result
Your tank uses a day0.30 dKH
- Daily dose to match
- 9.00 ml of Red Sea Foundation B (alkalinity)
- Per week
- 63.0 ml
- Kalkwasser can add
- up to 1.12 dKH a day
OK: Kalkwasser in your top-off water could cover this on its own, at 3.0 litres of evaporation a day.
Spread the daily dose through the day with a dosing pump, and retest weekly. Use grows as corals grow.
How do I measure alkalinity consumption?
Bring the reading to target, stop dosing, hold salinity steady and test again a few days later. The fall, plus anything you did dose in between, divided by the number of days, is the daily use. Turn that into millilitres with the product’s strength, as in the dosing calculator. Kalkwasser can only add as much as evaporates, because it goes in with the top-off water.
daily use = (first test - second test + rise from dosing) / daysdaily dose ml = daily use / (rise per ml in 100 litres) x (litres / 100)kalkwasser alkalinity a day = evaporation litres x 40 meq/L / system litres
Red Sea’s Foundation manual uses four days with no dosing; its four-part manual (2024) tests calcium after three days and keeps the dose if the change is under 2 ppm a day. Its four-part programme then doses parts 1 to 4 in the ratio 1 : 2 : 0.5 : 0.5, led by calcium. Triton adjusts its dose by dKH tests once the tank is stable.
Worked example: 300 litres losing alkalinity
- Alkalinity was 8.5 dKH, and 4 days later, with no dosing, 7.3 dKH. Use: 1.2 / 4 = 0.3 dKH a day.
- With a product that adds 0.1 dKH per ml in 100 litres: 0.3 / 0.1 x 3 = 9 ml a day in 300 litres.
- Evaporating 3 litres a day, saturated kalkwasser could add about 3 x 40 / 300 = 0.4 meq/L, or 1.1 dKH, a day. That would cover it on its own.
Can kalkwasser keep up?
Saturated kalkwasser (limewater) at about 25 C holds roughly 800 ppm calcium and 40 meq/L alkalinity (chemistry articles, seen in search summaries; we use the lower end). Bulk Reef Supply (2022) suggests mixing up to 1.5 teaspoons per US gallon, letting it settle, never letting pH rise by more than 0.2, and dosing slowly into high flow, ideally at night. Because it rides in the top-off water, a small tank in a humid room may not evaporate enough for a busy stony coral tank.
What are the limits?
Other calculators
- Salt mixGrams of salt for a batch, and what your refractometer or hydrometer should read.
- Salinity correctionHow much water to swap, day by day, at a safe pace.
- Water change effectWhat a change, or a run of changes, does to a reading.
- ATO reservoir safetyHow far salinity falls if a stuck pump empties the reservoir.
- Dosing from a test resultMillilitres to bring alkalinity, calcium or magnesium back to target.
- Unit converterdKH, meq/L, ppm, SG, ppt, litres and gallons, Celsius and Fahrenheit.
- Tank volumeLitres from the tank size, and the net water after rock, sand and sump.
- Heater sizeWatts for a UK room, split across heaters so one stuck on is not a disaster.
- Light hours and PARPhotoperiod, ramps, daily light and PAR by coral group.
- Electricity running costWhat the tank costs to run at the current UK price cap.
- Stocking and compatibilityCheck a list of fish against each other, the tank and your corals.