It is diffently a problem. I've had cloudy tank a few times, and I fix what ever I did or didn't do a.s.a.p. you gotta pin point the problem. I never had a so call "bacteria bloom" in my tank. The biggest reason some have it is because the filter is not big enough, not doing water changes as needed, over feeding.... The list goes on, and on. I didn't rise my polishing filter pad when I changed it one time, which caused white dusty particles to cloud my tank. I let the filter run for 1/2 an hour then shut it down cleaned the filter (canister) and did a 50-60% water change. Then did another 30% a little later. Cleared it up. Point is, it's a problem for the fish. Yes, it will usually clear up on its own. But it takes time for the filter to filter it all to clear it up.