Posted: Fri Dec 09, 2016 10:47 am Re: Advice Needed on Habitat Upgrade
That platform, as steve pointed out, doesn't really go very high. So in a bigger tank you would be sacrificing water and swimming space using it. Since you are just starting out, and while your res is relatively small, I would suggest a bit of planning (spending) for the future.
The cost for the basics will be somewhat the same (tank, lighting, filter and filter media) but I would skip the small docks/platforms and go straight into above tank basking areas. That way, even if your res turns out to be male and only grows about an inch or 2, you'll have minimum 50 gallons of water in a 65g tank. The basic idea is; a lightweight tank/box/enclosed space with some sort of ramp to sit on top of the aquarium for your turtle to bask in. You could, if you are a diy’er, even build one yourself.
If you decide to start with a 125g tank, then something a little less costly/complicated would be to use cork as a floating basking area. You'd be filling the tank about halfway with water and depending on what you put in the tank for decorations (what your res will allow you to put in,) your res would have about 60g of water to swim in. You can buy cork for aquariums and even cut it if needed.
Also, try to avoid using gravel. It's harder to keep clean and at some point your res will start to eat it.
All that said, one of the most important things to consider, and probably the most costly, is the filter. The ones that hang off the side/back of the aquarium might be ok now that your res is small, but they just aren't meant for turtles.