pond in my turtle cage

This question is cross-posted between rec.pets.herp and rec.ponds,
since I have found both groups to be helpful, but didn't know who to
direct this question to.

I installed a kiddie pool in my box turtle enclosure in my yard, with a
small circulation pump and embankment so the turtles can get in and
out.

I want to put plants and a few goldfish in the pond to keep the water
clean. The fish are to "process" the turtle waste, since the turtles
like to defecate in the water, and it often comes out in chunks (this
is per the suggestion of a rec.ponds person).

However, I am worried about transmitting pathogens/parasites to my
turtles. I would quarantine the fish of course, and soak the plants in
something.

Is there anything I should be on the lookout for?