This gas is of special importance to aquaculture because it is highly toxic to fish even in trace quantities, but there can be high contamination from industrial plants (dealt with elsewhere). Chlorine can be removed from water by stagnating the water open to air and also by use of filters such as the charcoal filter.
Both free and bound chlorine are toxic to fish Boyd, (1979) reports the values, obtained by white (1955), of free chlorine residues required to kill 100% 4 species of fish at 27°C:
| Fat head minnow: | 0.028 mg/l |
| blue gull: | 0.047 mg/l |
| Goldfish: | 0.074 mg/l |
| Golden shiners: | 0.079 mg/l |
LC50 for bluegil at 27°C - 0.021 mg/l of free chlorine.
