Looking to ID Algae in Sump

[CHEAPREEF]

I'm currently not running any filters or filter socks unless I scrub the stuff down then I put then in for the night to catch it all and take them out the next day. I'm running no WC's with ATI Essentials, everything tests out perfectly. All the corals the display looks great, colors and growth better than they ever have. Just this darn slime build up that needs to be cleaned out every 2-3 weeks.