If the cloudiness is indeed a bacterial or mild algea bloom the best solution I've found is to dose every few days with a bio-boost product like Nutrafin Cycle (I used another kind for a while but I can't find the bottle) and it seems to clear it up. I've never used them to start a tank but originally tried it on an overstocked 40g in a pet store that had persistent greenwater for over a month.
I will CAUTION, since you don't know what's going on I dont know how safe it is. I hear very love/hate opinions of these products. I have used it dozens of times in fresh and saltwater under a variety of conditions with no problems. Sometimes it was a last ditch effort. Also, I used it in tanks that had been running for years to some degree, not months. Oh, and a few customers used it to combat new tank syndrome related cloudiness and it worked.
In my area we get serious spring flooding and our tapwater changes drastically. Some months we have 0 ammonia, around now and as the floods dry off I've found over 2ppm and the smell of chlorine can become very strong (I don't have a test for it). To fight that I try to let my water sit out a minimum of 12 hours and OD on AmQuel+ or Prime. I mostly just use prime now but I think AmQuel+ was all I had for about a year.
Test the tap regularly! I test frequently this time of year because it's always bad. Less frequently or when I'm doing larger changes otherwise.
I second keeping a log, too. Can be very helpful with filter upkeep and moreso to track patterns or possible causes if your parameters are off. Couldn't figure out why I had a hint of ammonia in my catfish tank until I realized I had put off his WC
twice, whoops.
Wish I could be more help

Had a problem with really low pH and cloudiness a few years ago but it was just a 10g and I fought it and fought it with ammolock.. Eventually I got pretty tired of it and and decided just to do very frequent small WCs (treated with amquel and novaqua) and keep the light off more (few hours before and after work). It eventually stabilized with only one or two losses.
Good luck, keep updating