CRYSTAL CLEAR WATER
We need to determine the reason your tank is cloudy.
The first would be an algae bloom causing your water to have a green look. Micro free floating algae is a living organism that is flourishing in your tank. The main causes of an algae bloom are excessive light and or excessive nutrients and overstocking. It could also be your need to increase your water changes or maintenance routine. You can do that in two ways. Increase the percentage of water you are removing or the frequency.
Often in the early stages of establishing an aquarium you may experience a bloom caused by excessive nutrients that your nitrifying bacteria is unable to keep up with. You will need to do a massive water change to get rid of the algae but it will return if you don't follow this up with and second step.
There are a couple things that you can do. The first and simplest remedy is adding a UV sterilizer to your aquarium. They can be costly but they will do that job and eliminate any more blooms. Two of my show tanks have one and two don't. There are other benefits as well such as killing harmful bacteria and keeping your water clear of contaminants.
You can also do feed fast for a few days which is exactly what it implies.. Feed one day fast the next. This will help lower the available nutrients giving your beneficial bacteria time to multiply. To increase you bacteria colony you can also add bacteria from a bottle to help establish your colony. It's a good idea to add some at each water change as part of your maintenance routine.
The other issue contributing to your algae bloom may be your tank location. Too much natural light being close to a window or having your tank lights on too long may be factors.
The final thing you can do is simply wait. Your tank will balance itself out on it's own. It may take a few weeks but in time your aquarium will become crystal clear as it passes through each stage of the cycle.
If your experiencing cloudy water with a white look as if you added milk to your water you are experiencing a bacteria bloom. The cause for this is your bio load is larger than what your nitrifying bacteria can handle. This can be caused by cleaning your aquarium too well or adding too many fish at one time. This is the more dangerous of the two as your water can become toxic to your fish and could cause fish death.
The remedy for this is water changes. As you remove the water you will be diluting the ammonia and harmful toxins in the water along with diluting that milky look making your water clearer. Again.. Time will be your best friend. Keep up with your regular maintenance keeping an eye on your water parameters and in time your tank will clear itself.
Another water clarity problem is particles in the water. This could be caused by the food you are feeding, sloppy eaters or bits of debris floating in your water column. The food you are feeding could contribute to your clarity issue. I personally prefer feeding pellets as I find they do not dirty up the water like flaked foods do. It could be as simple as a change in the food you are feeding.
You can easily clean your water using a polisher, surface skimmer or even adding more fine fluff to your filtration system. There are many videos on homemade water polishers that are inexpensive and simple to make.
The key to having crystal clear water is understanding what is causing the problem and then addressing it with the remedy best suited to the cause.