High Cherrypie, hows the slime problem going - I can't offer any advice
on this issue (never had it happen to me "yet"). When you say fresh food
are you referring to fresh veg? I know that to much protein such as blood worm
and brine shrimp can cause a foam to develope on the surface of the water but this usually doesn't have a slimey feel to it . Hope you get it sorted.
Oh but doing the water changes that you are it should hopefully sort