Introduction and help needed.
Could it be after a water change or feeding? Or if the algae gets too much? Also no filter wool or anything like that exposed in tank?
If just occasional then it doesn't sound like a parasite (check gill plates are closing properly and not red), just something in the water that irritates every so often. Or if after feeding time, that should be fine.
Mine did it for several months before stopping.
Is the algae going away?
Last to check would be do you have water test readings? Ph, nitrates, etc.