Algae Eater pH levels

I have a community discus planted 125g tank, pH ~6.8, temp 86F, 
ammonium/nitrites/nitrates 0 that contains 9 discus, 3 small tetras, 2 SAEs, 
1 bristlenose catfish, 4 cory catfish, and 2 otos.   I want to lower the pH 
slowly to around 4 or 5 (the lower the better) to combat cyanobacteria 
without resorting to medications.  Discus love low pH but I don't know what 
the lower tolerance levels are for the algae crew.  Has anyone kept or 
temporaily mainained SAEs, bristlenose or otos at low pH?

Rochelle Williams
williaro at ftmcphsn-emh1_army.mil