Cyno is a bacteria not a algae as it's commonly called. and that's why stuff like "red slime remover" works. It contains mostly ethromycin which is a antibotic. The main cause of it is from high nutrients in the water, caused by over feeding,( expecally if you feed unwashed frozen foods which also add phosphates to the water.),and not fully cured rock.
without using chemicals/antibotics the best way of removing it is to syphon it out or keep a power head on it to free it from the sand/rock. and then trapping it in a filter bag. try cutting down of the feeding and feed only small amount a few times a day this along with the physcial removal will get rid of it.
HTH
chuck
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