redearslider.com

what do I need to make a cascade in the tank? I want to make one, but they didnt know how to make it in the pet store

also, I need to get a new filter. Which one of the next ones would be better for a 20 gal tank, and what else besides the filter do I need to order?

By cascade you mean a waterfall? If so, you could get a hang-on-tank (H.O.T) filter like an Aquaclear (there are others, though). I used an Aquaclear 70 on a 20-gallon-long tank and it worked well. It is noisy, though, unless the water is fairly high. You can make it even more quiet by using aquarium silicone to attach a piece of plexiglass to the lip to lower the distance the water has to fall into the tank. The Aquaclear came with all the media, but you may want to order extra (the carbon, for example) if you're buying the filter online.

yes I mean a waterfall. Aquaclear is like a filter? and can I put decorations on top of that? like rocks or plants, to make it more natural.

They have a waterfall filter in a lot of the pet stores that I go to. It looks fairly natural... at least the pic does.

I wrote a short review awhile back on this filer which is waterfallish. It wasn't the best. It looked nice, but it should not be the sole filter for your setup.

http://www.redearslider.com/forum/viewt ... highlight=

I added this to my old terrarium to help water circulation and purity. The tetra stuff in general is not the highest quality but for convienance and ease of filter replacement they're tops.

http://www.tetra-fish.com/sites/tetrafi ... 76&cid=282

You can take these and set them on the bottom of the tank (this if your waterline isn't higher than the filter with the filter sitting on the bottom) and stack bricks or rocks up against them. It creates a nice little waterfall.