There are several reasons why the water in your aquarium might be on the cloudy side, and many aquarium shops might try to sell you all kinds of expensive chemicals that promise to clear that water right up, but most of the time those chemicals are completely unnecessary and sometimes can even do more harm to your tank then good.
Here we have listed the top 5 most common reasons your fish tank is cloudy, and what you can do about it.
You didn’t rinse the gravel and ornaments before placing them in the aquarium.
New aquarium gravel and ornaments can often have a lot of dust that comes with them. Placing them directly in the aquarium without rinsing them first can very quickly dirty up your water. Have no fear though, because after doing a few water changes and running the filter for a while this should clear up in no time.
Now sometimes even though you did rinse the gravel, you may not have rinsed it thoroughly enough and there could still be some residue and dust on the gravel and when you go to fill up the tank it still ends up looking like a cloudy murky mess in there. Once again though, after a few water changes you should be squared away.
So, you got your newly set up and your aquarium seems all squared, but then a few weeks later or a few days later, or sometimes even a month or so later all of a sudden, your tank has this weird milky look to it. This can be sometimes caused by a bacterial bloom.
Now a bacteria bloom is completely harmless, and it usually clears up after a day or two, so there is no reason to worry. This is just a part of the cycling process, and it's just the beneficial bacteria settling in and colonizing in your tank. This milky appearance should disappear with time. My best advice for this is to just wait it out and try to avoid doing water changes until the bacteria settle.
Not properly gravel vacuuming
If you're not doing proper gravel vacuuming, you could have excess food or debris that was left in the tank or even decaying plant matter that can also cause that kind of dirty appearance to your tank water. A few good water changes with your gravel vac should resolve this quite easily.
The Aquarium is overcrowded
An overpopulation of fish can quickly dirty up your tank and leave you with poor water quality. If possible, ideally you would move some of the fish into a different aquarium, but if not, you may find you will have to do more frequent water changes or upgrade your filtration system to keep your water looking crystal clear.
Overfeeding your fish
This is probably one of the most common problems for people new to fish keeping, and one of the easiest issues to solve. We're all guilty at some point in over feeding our fish, as it's fun to watch our fish eat so we like to throw a lot of food in there. But, because many of the fish that we keep are so small, we don't realize how much just a few pellets per fish really is.
I don't know how many times I've seen somebody just throw a handful of fish food into a tank that only has three or four two-inch long fish in there, they're not going to eat that much food, so naturally it's going to clog up the aquarium. So, if you notice your fish tank looking cloudy and dirty after feeding, you may want to cut back on how much or how often you are feeding your fish.
Now of course there can be other reasons you may be dealing with cloudy water, such as extremely hard water, or having high phosphates, but that will have to be for another time.