Moving from 65F to 80F will not affect the bacterial load. The same population that detoxifies ammonia from goldfish will do the same for discus.
One concern would be that ponds support other organisms that may harm aquarium fish. There are larval forms of insects that can predate. You might want to vigorously squeeze the sponge out and move it to a bare tank to see if anything grows out. (Don't worry, vigorously squeezing does not wipe out the bacteria.) If nothing grows out in a week, you're good to go. Nothing in life is guaranteed, but that would be a reasonable approach.