Are you sure that it's really acting as an algaecide, or just helping the more efficient plants out-compete algae? (I think I've been reading too many Tom Barr threads... I've got CO2/photosynthesis limitation on the brain LOL)
I'd bump it up to 30ppm and see what happens, personally. That or permanently decrease the wattage (the last is really what I'd do- but that's my low-light bias coming through
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