G.P.H. means gallons per hour. It's basically how much water that particular filter can move in an hour.
Depending on how big your turt is now, you're gonna need a bigger tank sooner or later....If you can afford it, why not get a canister filter that can be used when you get a larger tank?
http://www.bigalsonline.com/BigAlsUS/ct ... sterfilter
or:
http://www.bigalsonline.com/BigAlsUS/ct ... sterfilter
The 4 plus is only a simple mechanical filter...not very flexible, and when you get a bigger tank, it'll be useless, unless you can use it to supplement another small filter which, in the end, you'll have spent as much money on two small filters as you would on one large (and better) filter.
