cyano and Flow ?

siphoning into a filter sock works great for cyano. Cutting a couple hours in your photo period will help slow it down. But you must remove the cause, which I'm sure has to do with your tap water, as well as too many nutrients from feeding/waste from fish. Use GFO moderately at first. Don't go too fast with it. It's better to use less, and change it out frequently. Your GFO can get exhausted rather quickly if you have high PO4's. So you will want to change it out every couple of weeks, or until you get a feel for how it works with your tank. For myself, if I see algae, I know my GFO is exhausted, so I refill.