We have always used a mild dish-washing liquid mixture to get rid of aphids, but I would think that wouldn't work well with your turtles We also have (in the dirt garden) planted marigolds and other plants that will drive away the aphids and such (it didn't do anything for the grasshoppers last year, they ate the marigolds too!)

I know this isn't much help, but I thought I'd put it out there for you to consider anyways.

I have the Urban Aquaponics Manual by Gary Donaldson - from down under. He just says to spray them off with an organic spray (if you have an open-loop system) - I guess that means plain water if you don't.
Quote Originally Posted by Urban Aquaponics Manual, pp.87-88
Pest Control
Aquaponics growing requires a different approach to pest control.

Fortunately, raised grow beds encourage close inspection of plants so, if you encounter grubs, leaf hoppers and caterpillars, you simply pluck them off the plants and throw them into the fish tank.

Fish seem to appreciate the occasional slater or earwig too.

Insect pests like mites and aphids can often be washed off plant. If your growing systems are open-loop (non-recirculating), you can even apply an organic spray.