I was doing the same thing ...I found that it just started appearing over more of the rocks ...I really think you need too be aggressive in trying too remove as much as possible each day ...I also found that using the aquavac seemed too help more as opposed too siphoning...and have you thought about adding a power filter too your tank rather than letting it just go into the overflow and filter socks ...doing that at night and pulling the filter before the lights come back on ....I know your getting the pods and the bacteria ...but there's still a few things you can do in the meantime ...I know how hard it is too look at your tank when it's covered in dinos or cyno ....I even thought if I left it it would burn it's self out ....till I couldn't stand too look at my tank anymore....