Mustard algae experience

[jhm]

One other thought, after a thorough shocking should I replace my cartridges, or can I get away with cleaning them? It ain't cheap to replace them.

[chem geek]

If you've got fairly even flow through your cartridges, the high shock level should be sufficient for killing algae in them. You could always clean the cartridges rather than replacing them. Algae won't like detergent, but it's really the chlorine that kills them.