My koralia 3 hardly puts out any suction at all. My fish swim right up against it and don't even seem to notice it. I guess if a fish was small enough to actually swim inside the guard it could be in trouble.
However....if you should turn off your Koralias make sure you check that the pump is clear of any small fish. I had a blenny that liked to sit inside the cage whenever it was off.
lmao that is a story and a half...Sorry for your blended blenny...I think my watchman goby might have gone carpet surfing as KathyC would say...I haven't seen it in a while..