My son has a 10 gallon tank with glowfish and danios and neon tetras but it stays so cloudy that it is unreal?

ive tried daily partial water changes, vacuuming the gravel the ammonia level and ph are perfect and the nitrate level is ok...and it seems like some sort of ooze grow over night...does anyone have any ideas...and what is that stuff that looks like a clear kind of ooze that is coating everything, i have oscars and cichlids and my tank does not have this problem...thank you for any help that u may be able to offer...