Algae needs
excess nutrients to feed off of. Mostly it's levels of
po4 above .03
ppm that causes algae blooms.
No3 plays a small role also but IME only if it's above 20
ppm.
Even though you may test
po4 in the tank at 0
ppm the algae may be consuming most of it to give you a false reading.
Have you tested your source water for
no3/
po4? (before and after mixing your salt)
I agree with Kurt that you are heavily overstocked for a 55
gal even if all your fish are juveniles. Even if you are maintaining
no3 levels with constant
pwc the amount of food needed to feed that many fish is going to contribute greatly to excess nutrients that feeds the algae.
The Protien Skimmer can't come soon enough. You need a powerful skimmer to help reduce
doc, clean your canister weekly, and reduce your fish load to 12" of adult length or you will be fighting algae forever.