🧪 Water chemistry
Aquarium & Pool Chemistry
Calculate how much chlorine product raises your water to a target ppm, plus salt for a target salinity. Press Calculate.
About the Aquarium & Pool Chemistry
Chlorine dosing is a concentration calculation. One part per million is one milligram of active chlorine per litre. To raise 10,000 litres by 2 ppm you need 20,000 mg, or 20 g, of active chlorine. A 10% sodium hypochlorite solution contains about 100 g of active chlorine per litre, so the dose is 200 mL.
The same arithmetic works for a small aquarium, but the products and targets are very different. A pool might run 1–3 ppm free chlorine; a planted aquarium should have essentially none. This calculator reports the active ingredient required and the product volume; always follow the product label and never mix chlorine products with acids.
How the calculation works
- Active chlorine (mg) = volume (L) × (target − current) ppm.
- Product (mL) = active mg ÷ (product strength % × 10).
- Salt (kg) = volume (L) × target salinity % ÷ 100.
- 1 ppm = 1 mg/L.
Reference values
| Product | Active chlorine | Dose for 10,000 L +2 ppm |
|---|---|---|
| Bleach (5%) | 5% | 400 mL |
| Liquid chlorine (10%) | 10% | 200 mL |
| Liquid chlorine (12.5%) | 12.5% | 160 mL |
| Calcium hypochlorite (65%) | 65% | 31 g |
| Dichlor (56%) | 56% | 36 g |
Worked example: a pool and a small tank
A 10,000 L pool at 1 ppm free chlorine needs 10 g of active chlorine to reach 2 ppm. At 10% sodium hypochlorite (about 100 g of active chlorine per litre), that is 100 mL. For a 100 L aquarium, raising chlorine by 1 ppm would need 100 mg of active chlorine—far too much for a stocked tank; use a chlorine remover instead.
The arithmetic is the same, but the targets and products are not. A pool might run 1–3 ppm free chlorine; a planted aquarium should have essentially none. Always follow the product label, never mix chlorine products with acids, and test with a kit suitable for the water you are treating.
Frequently asked questions
Related tools
Safety note
Chemical quantities here are planning estimates, not a substitute for the product label or a qualified professional. Follow the manufacturer's instructions, use the recommended personal protective equipment, and keep chemicals out of reach of children. Test on a small batch or area first.