turtle tank filter

hau kolas..got a bit of a quandary here..I've acquired a small painted
turtle who has been living in a 20G L
tank with about 5 gallons of water and "land" areas at either end of the
tank. Anyway, being as the water area
is pretty small, threw a fluval 1 plus internal filter in there. Long
story short, turtle has grown and IMO
needs a new tank. Looking at a 40G long in the near future. Never really
happy with the internal filter, I've decided to
put a small canister for the new tank. Looking at either a fluval 104 or
AP rena filstar xp1, which seem to be smallest
canisters I can find w/o a whole lot of effort looking into it. Fluval
104 or 105? 5 series seems to have about a $20.00 jump
in price from 4 series models. Is it really worth it?

At most I'm looking at 15 gallons of actual water in
this tank & what's in the filter and pipes. is the fistar going to have
too much flow for the turtle in such a small volume of water?
Can I add a valve or spraybar to disperse this w/o too much back pressure
on the filter?
I've been a fluval loyalist on my fish tanks, but not so sure on this
turle project.
Relatively uncharted territory for me..any suggestions on setups people
here may have? Turtle is relatively small, shell
circumference is 6.5" cross shell, won't cooperate enough to measure
lengthwise.

TIA

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