If you have t5s you may be due for a change out. I was battling cyano
for a good 3 months and did it all: weekly water changes, siphoned it all off the sand, scrubbed it off the rocks, decreased feeding frequency and amount, decreased photo period, increased flow and ran GFO
Until finally I read an article that older fluorescent bulbs start emitting more red the older they get and the bacteria thrives w more red wavelength. I changed all four bulbs and after the next WC
it never came back.