Help! Our fish reservoir river is concrete cloudy and I can't amount out why?

we bought a 20 gallon tank over the summer put about 12 fish in and cistern looked beautiful. After 3 mnths we cleaned it, did 1/2 water change and cleaned every entry in tank. Tanks got genuine cloudy and I don't believe that I am overfeeding them! I changed the filter and that didn't help either. We then purely cleaned again last week and for about 3 days tank be crystal clear now it is worse than the last time. Can anybody tell me what i might be doing wrong.
The filter probably wishes to be cleaned!
The reason the reservoir is cloudy is because you cleaned it. I am assuming you used tap water to clean eveyrthing contained by the tank including the filter, you should never do this. Contents of the tank should be washed surrounded by water from the tank and that includes the filter, adding a foreign filter only made matters worse because the new filter did not contain any of the positive microbes needed to maintain a tank.
Do not put any more fish in this cistern as it needs to mature after the cleaning, this will take at smallest 3 or 4 weeks do daily partail water changes of approximately 10% remembering to either leave the new marine to stand for 24hrs or add a substance which gets rid of the chlorine.
The water should leisurely clear as the tank matures.
Get yourself a test paraphernalia and check the ammonia and nitrite levels before adding any more fish.
sometimes its the rock, after you russle the rock it gets cloudy. I got de clouder drops and it helped contained by 2 days.i had same problem as you.
Its a bit more expensive, but use activated carbon, instead of that do nothing charcoal, in you external filter.you only have to use 1/3 of what amount of the charcoal you use, and you can re-activate it by putting it in the oven, and heat it up..
Answers:    New Tank Snydrome! Changing out your filter and doing adjectives that cleaning at once and everything in the tank removed all the moral bacteria. You are now having to start another cycle. It should clear rear legs up on it's own in several days but once again you have to watch your ammonia and nitrites level.

Terrible advice in the above answers! I wonder where relations come up with some of their answers. Do NO MORE cleaning at this time.

Never clean everything like that again. Clean the reservoir but leave the dirty fiter media alone. Or...change the filter medium but leave the tank alone.
check to see if your power filter needs verbs or your ph levels in are to hight are low you can refilling it but i would do this.
I wil give you the short answer which is the account of things you are doing correctly

1. Fish need water
Clean it again. You have to keep cleaning it.
Your reservoir should be on a weekly cleaning schedule including gravel vac removing only 25% of the water and replacing. Not every 3 months. Also, everything contained by the tank does not need cleaned. Doing this removes the beneficial germs in the tank causing a bacterial bloom.
Here is an article that explains the germs cycle.
http://freshaquarium.about.com/cs/biolog...

Also changing out filter removes much of this\ beneficial bacteria and really should only be changed when "falling apart" regardless as to what the box say.

Your fish need this bacteria removing it forces the biofilter to mass produce the beneficial germs causing a Milky or cloudy bloom. It isn't harmfull to your fish. It will clear on its own, however you have to stick to the weekly 25% NO MORE water variation including vacing.
What type of fish are these?   What class of fish cistern?   How do fish reproduce or how can you relate whether they will reproduce?   What small fish can I maintain contained by a 20 gallon saltwater cistern?