Found fish in backyard, not sure what to do?

We just moved in to this house in California and there was a pond in the backyard. There are four large fish and several small ones. I am pretty sure that the small ones are comet goldfish, two of the larger ones are also comets, one koi, and a bubble eye. They apparently have survived for three or so months without human care. I have a koi and other goldfish in the house and was wondering if I should put the water purifier liquid I use for them into the pond and if it would be okay to put my koi and comet goldfish into the pond.