Sounds like you're dealing with the same thing I am, mystery cyano
. Low low nitrates and no phosphate and still getting a cyano
bloom. Right now all my water flow is at top layer and nothing down low so mine is a flow problem at the sandbed level. Not really a mystery, but I'm lazy
and calling it mystery is more fun. Although I do think some tanks will go through a cyano
outbreak just like diatome outbreaks after cycling. Other than that, what is your tank setup?