My 10 gal. fish aquarium has suddenly become cloudy, a few days after I cleaned it. What could be the problem?

it is because you kill all of the beneficial bacteria that is keeping your fish alive. fish = waste = nitrite + ammonia = [bacteria] nitrates. explanation? fish produce waste which puts ammonia and nitrites into the water. your filter contains bacteria that breaks down these chemicals, both of which are highly toxic to your fish, and turns them into nitrates. nitrates are still toxic to your fish, but not as harmfull as nitrite or ammonia. a build up of ammonia, nitrites or nitrates can and will kill your fish. the only way to rid the water of nitrates is by water changes. but, water changes are not as good as most people think. especially when you are using an undergravel filter, most of the nitrates are sitting on the gravel, rather than lurking in the water. so, instead of water changes, you should vaccume your gravel untill your gravel is clean/20% of your water in the tank has been siphoned out. this means that it counts as your weekly water change. so, to wrap up what i just said, you should be vaccuming your gravel instead/aswell as changing the water. you should not be completely taring apart your aquarium every week. you should do what i just explained with the vaccuming onece a week and change the filter media once a month. do not change any water or vaccume the gravel straight after/before you have exchanged the filter media or you will get rid of all the bacteria. most of the benificial bacteria lives in your filter media, however some lives on ornaments and in the gravel. you should almost never sompletely break down your tank. the reason it is going cloudy is because you are getting a bacterial bloom. this is normal when you are cycling your aquarium. every time you break down the tank, this is what you are doing. you are starting from scratch and cycling the tank all over again. your fish must be very hardy to have survived all this time. most of the time most fish will die from this, it is very hard on the fish. for more information of cycling the tank, here is a site about cycling (i support fishless cycling over cycling with fish):

http://www.algone.com/fishless_cycling.php

for more information, you can google it, or ask a separate question here on yahoo! answers.

best of luck, i hope this has helped =]

You are over cleaning your tank.

You should only be removing 2.5 gallons of water when cleaning.

When cleaning your tank, scrape the sides of the glass. Unless your decorations are dirty and I mean you can see the dirt, don't clean them. Use the gravel syphone and lean the gravel. Careful to only remove 2-3 gallons no more. Fish remain in the tank. Mix your new water and add to the tank. DO NOT remove the filter itself to clean it unless it is a mess.

If you are totally removing everything and replacing it you are killing off the beneficial bacteria your tank needs and tosses it into a "bacterial bloom". This means the biofilter (what you cannot see) is working overtime to create a new biofilter for balance.

Try this the next cleaning (remember once a week or every two weeks only)

how did you clean it? gravel vac? water change? Remember when cleaning to remove only 20-30% of the total water to avoid putting a strain on the fish and the biological filter. it could also be free floating particles from the gravel floating around, another good reason to gravel vac.

Was it just a water change where you cleaned the gravel and etc.. just the typical stuff?

It's just a bacterial bloom and should clear up on its own.

It happens in my tanks as well if I do a largish water change. It isn't anything to worry about if you have a good mature, cycled tank.

mine does that when I clean it too. after a few days it clears up. I was told its because you mess up the biological balance or something like that.

they sell stuff that helps clear it up though