Posted: Mon Aug 25, 2008 12:33 pm
Greetings and welcome to the forum! If your turtles can look forward to a 300 gallon home some day, then I'd say they are pretty lucky turtles.
On changing the water, the frequency depends on a lot of things - the size of the tank relative to the size of the turtle, the size and quality of the filter, whether you feed them in the tank or not. If the water smells bad or looks bad, then it's been too long between water changes. The best way to tell if the water needs changing is by testing it for ammonia, nitrites and nitrates. You can get a kit for testing (I recommend the Master Freshwater Test Kit by Aquarium Pharmeceuticals, available at most pet stores and contains lots of testing solution for many months of tests). Some of the bad stuff that accumulates in a tank is invisible, and the tests are the best way to detect it.
Untsmurf gives good advice. Read everything on the site - it's a goldmine. Then, you'll no doubt have specific questions. Come back here and ask and you'll get the help you're looking for.
by the way, we'd love to see some photos!
SpotsMama