Okay, the biofilters and just about any surface of the tank have bacteria colonies but the filter media has the most of it, if that isn't sufficient or the filter bacteria takes a knock for whatever reason then free floating bacteria can start growing to eat the extra nitrite or ammonia which gives the cloudy look. Generally isn't harmful but is an indicator that something isn't completely right.
It could be your substrate too, if it's got excessive detritus and it's stirred up then it could cloud too.
Do you have products like "Seachem stability" available? This will help seed biofilters in the tanks bacteria especially if you get a new filter.
Frequent water changes will help a bit as well