There is white slimey stuff in my sump

Yes, pineapple sponges. I'd not worry too much about them. If you have a ton of them just remove them by hand.

At what point do I determine that there are too many? Can they be bad and contaminate my water at some point? I must now have a few hundred, just over a few weeks' time. I assume it's them that's making my sump water a bit slimey?
 
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