Happened to a friend of mines. He added calurpa and put a phos zorb in the tank. Also did a minor water change or two. Like ost cases one day- bam it was gone. Like magic I tells ya. As long as sun isn`t hitting the tank, I would limit light cycles to the minimum required and maybe ad a phoshate remover. i am kind of opposed to water changes as they can recharge the algae that we are trying to get to deplete. The diatom filter was going to be the next step, but in the week we fooled around it cleared up. They are not a plug and play filter- but nothing else can polish water like a diatom. The fact the design hasn`t changed in 40 years should tell you something. Then again the fact few use them should tell you another! It works great but it is a little overwhelming to some folks to break out very often.