I got an elite stingray filter for a ten gallon.I got the medium filter, which says its for up to five gallon tanks, because I didn't want it to be real strong. Its too strong, my poor goldfish has to swim constantly so she doesn't sick to it, so I turned it off. I read somewhere you can put nylon over the filter to keep fish from being sucked into it. Does the nylon also make it weaker? Will anything make it weaker? Also, how well do undergravel filters work if at all?