I gave up on aquariums for my turtles.Simply because I don't like the width in the ones I try.
Turtles get off the basking dock & clunk onto the sides.My turts are now in a kiddie pool,till I move then they'll have an indoor pond.
I found these instructions for an outdoor one,in case someones interested in making one (either for turtles or fish).
The link shows a pic of the turtles previous setup first then scroll down& you get to see a nicely made pond.
Pics go with each instruction.
Backyard Turtle Pond / 2001-2004