I had really thick mats of cyano on my rocks and sand bed. It was so bad my corals started closing. After I got my two wp40s I did a strict lights out with NO feeding. I was so tempted to peek at my tank in those 3 days but I didn't. I skimmed wet the whole time and used a filter sock which I changed out every day for the 3 days. I am now cyano free. Checked phos and I'm at .25 (used to be at .50) so I plan on getting a gfo reactor some day.