Reef dosing calculator
Your test came back low. Work out how many millilitres bring alkalinity, calcium or magnesium back to target, with two-part and Red Sea four-part, split over days so the rise stays gentle.
Formulas and sources last checked . How we check
Calculator
Result
Alkalinity, in total24.0 ml
- Product
- Red Sea Foundation B (alkalinity)
- Raise by
- 0.80 dKH
- Dose
- 24.0 ml
How do I work out a dose from a test result?
Every supplement has a strength: how much 1 ml raises its parameter in 100 litres of water. The dose is the shortfall divided by that strength, scaled up or down for your net water volume. If the shortfall is bigger than the safe daily rise, the dose is split equally over enough days to stay within it.
ml = (target - test result) / (rise per ml in 100 litres) x (litres / 100)days = shortfall / largest daily rise, rounded up
Worked example: alkalinity at 7.2 dKH in 300 litres
- The target is 8.0 dKH, so the shortfall is 0.8 dKH.
- Red Sea’s Foundation manual says 1 ml of Foundation B raises 100 litres by 0.1 dKH. For 300 litres: 0.8 / 0.1 x 3 = 24 ml.
- 0.8 dKH is within Red Sea’s 1.4 dKH a day and above the 0.5 dKH SPS pace, so an SPS keeper would give 12 ml today and 12 ml tomorrow, testing in between.
How strong is each product?
| Product | Rise | Where it comes from |
|---|---|---|
| Red Sea Foundation A (calcium) | 2 ppm | Red Sea Foundation manual: 1 ml in 100 L raises calcium by 2 ppm. |
| Red Sea Foundation B (alkalinity) | 0.1 dKH | Red Sea Foundation manual: 1 ml in 100 L raises alkalinity by 0.1 dKH. |
| Red Sea Foundation C (magnesium) | 1 ppm | Red Sea Foundation manual: 1 ml in 100 L raises magnesium by 1 ppm. |
| Red Sea Reef Care four-part, part 1 (calcium) | 1.4 ppm | Red Sea Complete Reef Care manual (2024): 1 ml of part 1 in 100 L raises calcium by 1.4 ppm. |
| Red Sea Reef Care four-part, part 2 (alkalinity) | 0.1 dKH | Red Sea Complete Reef Care manual (2024): 1 ml of part 2 in 100 L raises alkalinity by 0.1 dKH. |
| Tropic Marin All-For-Reef (calcium) | 0.4 ppm | Our arithmetic from the label strength of 20,000 mg calcium per 500 ml (label seen via retailers): 0.4 ppm per ml in 100 L. |
Where do sources disagree?
| Topic | What sources say | Our reading |
|---|---|---|
| Which test leads the dose |
| Follow the method you have chosen. For one-off corrections, alkalinity is the reading that matters most for stony corals. |
| How fast to correct |
| Use Red Sea’s limits for soft corals and LPS, and the gentler pace once you keep SPS. |
What are the limits?
Other calculators
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- ATO reservoir safetyHow far salinity falls if a stuck pump empties the reservoir.
- Daily consumptionHow much your tank uses a day, and the daily dose to match.
- Unit converterdKH, meq/L, ppm, SG, ppt, litres and gallons, Celsius and Fahrenheit.
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- 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.