Diffuse the current with one of the following ideas or something similar. put a piece of PVC pipe on your output, and drill holes in it to direct and regulate waterflow back into the tank. You can play with the pipe until you find what you like without much cost involved at all. Simpler but less workable, place sponges over your input and output. I have this set-up on my guppy breeder which carries something close to 15 times actual turnover of tank volume per hour.
dave