HI so my 20 gallon turned a really thick green a couple weeks ago. It had fish which it no longer does but it was cycled and fine for months. After it turned green (parameters were fine) I did an 100% water change and did my best to clean the filters (not sure I know how) I have a top fin 20 and a Penn Plax Cascade 300 in there. Now I refilled with water cleaned decorations. Took out a dying Amazon Sword. Put in neon Tetras and again it's slowly turning green. Last time it only took 2 days to go from fine to extremely green. This time it's slowly taking a while and I can't figure it out. I cleaned the glass and tried API AlgaeFix with no results. Any advice? Parameters still appear ok.