I remember I had some and I stopped feeding them when I got bored of them and they never died
You can't really clean their water but you can move them to a bowl or something and then clean their tank.
If I remember right actually, you can buy a water purifier packet from the makers and maybe that can clean the water?
As soon as I saw this thread I thought of Lex. Her username is Sea Monkey.
I did this too.
Anyway. I had some when I was younger, and we bought them in a kind of pack, which came with everything we needed (tank, water purifier, etc). I think the water purifier was the closest thing we ever got to cleaning the tank, since a) it never got that dirty and b) they never lived that long anyway.
They're fun pets though.
You want redemption?
Find another way to stand and fight.