The slime/goo is bacteria eatin' away and rotting your clones. Wipe the slime/goo off (I'd clean 'em w/peroxide) and thoroughly clean the inside of your unit. Use fresh distilled or reverse osmosis water. Tap water has too much bad stuff in it. Keep your clones clean, warm and wet and they'll thrive so you can put 'em into pots of pebbles or soil or whatever medium you're usin'.