I have a 55 gallon tank. Its been up and running for about a year and 7 months years now.
But here lately I have been having some troubles with it. It keeps getting cloudy and my ammonia levels are high. I was told to add moss balls to my tank and do a 30% water change, so I did. I still keep losing fish, My tank is still cloudy and my ammonia levels are still high.

I have 2 AquaTechPower Filter 30-60, a 200 watt heater, and bubble wall.

Any advice to help me clear up my tank and lower the ammonia levels will be greatly appreciated!! Thanks in advance!

Do you have too many fish?
How is the PH level?
Has anything changed recently?

This is a very informative page that should help you:
About.com.

I have 6 Skirt Tetra, 4 Lamp Eye Tetra and 1 Plecostomus. About how many fish can I have in the 55 gallon. Do I have to many now? The PH levels are good. The only thing different I have done recently was added a cave from the pet store. Could that be my problem?

Well the first thing to trouble-shoot increasing/decreasing levels is to identify what has changed. Since you have recently put in something new, I would take it out.

Have you ruled out any diseases? How do the fish look once you take them out after dying?

I have a 45g Pentagon Corner with 3 New World Cichlids and 1 Pleco. I was always under the impression that 1" of fish per gallon of water was a safe rule. Not sure the sizes of yours but you have 12 in that tank.

Any mating pairs?

Now wait... you added a cave recently... Did the problem start shortly after that?

I had a tank going real well for years and bought something, washed it off, and added it. A day later I was having problems with the water. I removed it and the problem cleared up. I soaked it in a bucket of water for a week then washed it off with clean hot water. It seemed to be good then.

Maybe try removing that cave and see how it goes.