I have been wondering the same thing.
After a brief google session, I have come to the conclusion that perhaps it would be best to start over and remove the soil.
Potting soil contains manure, tons of it. Potting mix contains none.
Potting mix is designed for growing plants in containers. Potting soil is not good for containers.
Potting soil is designed to handle oxygen and water exchange more effectively for plants.
I don't know what your heading into, but I would leave the fish out of the middle of it.