Slimey Purple stuff!

[Ruth]

Sounds like cyno to me. Try to syphon out as much as you can, take the rocks out and scrub them, cut back on feeding. If you have sponges anywhere in your system make sure they are cleaned daily or just remove them for a while. As a last resort you can use chemi clean but if you don't know where the nutrients (ie overfeeding, sponges) are coming from it will just come back.