HI:
i'll start by saying this is a sign. cyanoalgae is an indicator of nutrient problems w/ your water. So first off check out your water parameters, do water changes and clean to get your water back to perfect.
W/ that said cyanoalgae is a misnomer its actually a bacteria (a blue green called cyanobacter), and therefore is suspectible to antibiotics. The red slime algae removers are erythomycin, and if you do use an antibiotic ensure you do water changes and the like after your done, becuz once you elimiante the slime algae, if you don't eliminate the problem it will right back.
Read up on it
frank