My husband wants to install a fish tank in our son's room. Our child is 8 months old. I worry because I find the monotonous motor sound of the filter loud. Doesn't it hurt my baby's rest? He is never in complete silence when he is asleep, is this some kind of noise pollution?
Though noise pollution certainly is an issue for some urban neighborhoods (for example those living near airports). I don't think your situation is one to worry about.
A certain amount of background noise isn't harmful. In fact, some babies like to sleep with soft sounds, just as some need a nightlight on. Unless your filter motor is a lot louder than the one in my child's room, the sound becomes a background hum.
The real answer, however, will come from your baby. If his sleep is disturbed, you will see it in his behavior. He will awaken more often, change his sleep pattern or show more sleepiness or irritability during the day. My guess is you'll see no change and the fish will be fun for your son to watch. After all, children do have a knack for sleeping through practically anything. Hence the expression, "sleeping like a baby...."