Elevate your skimmer about 4" to be able to get control of the micro bubbles activated by sand, sock, or cycling. Skim out a controlled wet then slowly lower the skimmer to 3" then 0". This will take about 3 days to work out what ever has caused the skimmer to overflow. I use various Tupperware or food storage containers to elevate. Had the same issues after using Chemi Clean that completely removed any trace of cyano.