I can understand turtle owning on a budget

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Personally, I think that as you only have a hatchling now you can skimp on the filter (because he's not producing much waste at 1-2 inches) and should go for the larger tank... that way as he grows you can budget for the better filter as opposed to the larger tank and the larger accessories that go with said tank. So say you bought a 40 or 50 gallon tank, you could still get away with a filter rated for closer to that size tank as opposed to a canister filter to start with, and then upgrade the filter as you go. Items like basking docks aren't expensive. And most other things like the lights and thermometers can carry over from tank to tank so the big items are really the stand (if you get one), tank, and filter... at least that's how I look at it.