Hello! Welcome to the hobby and forum...
I see you got a 5 gallon tank. 5 gallons is a but small for any fish, especially neon tetras or any shoaling fish. These fish should be kept in a densely planted 20 gallon tank. 10 gallons is an absolute minimum but 20 gallons is ideal.
The reason your tank is clouded is due to the fact that you did not cycled most likely. What you have to do is test the water parameters with a liquid test kit like the API master kit and test for ammonia, nitrites, and nitrates. I would also recommend researching more on the nitrogen cycle because that is what is going on. To put the nitrogen cycle in a very short way, what happens is basically a fish or fish food produces ammonia which is highly toxic to fish and then turns into nitrite which is still very toxic to fish... After ammonia turns into nitrite, the nitrite turns into nitrAte, which is less toxic but should always be kept below 20ppm. A good amount to keep it at is 10ppm, but lower is better... I would do a large water change of about 75% and keep doing this until you stop seeing ammonia.
If you have a filter where you keep changing out a cartridge, I would recommend not changing out the filter media until it is literally starting to fall apart. When you get rid of filter media, you are also getting rid of ANY bacteria in there...
Please do not think I am trying to point out every thing you are doing wrong and putting you down. I understand how it can feel when someone keeps bringing up things youve done wrong but I am sincerely just trying to help in the kindest way I can...