A note of caution about using bleach to control algae. My greenhouse has a gas
heater. The instructions for the heater warn against the use of chlorine
bleaches when the heater is in use. The fumes from the bleach can react with
the metal of the heat exchanger at the high temperatures that exist when the
heater is operating. This can, according the the instructions, greatly shorten
the life of the heat exchanger.

David