SLOW DOWN. You have 5 posts going at the same time, all saying the same thing. YOUR GOING WAY TO FAST!!!
1st) let your tank cycle, slow down on the water changes, do not stop them completly, but abotu 10% once a week should be ok through the end of your cycle.
2nd) once the cycle has completed add livestock slowly.
(Cycle); Ammonia will spike (rise) and then drop off, next Nitrites will spike and drop off followed by Nitrates. When these nitrates drop your tank is cycled. Basically, you are waiting for bacteria to build up in the rock and substrate that converts the ammonia (waste in tank) into non harmful matter.
3rd) Livestock, first is a clean up crew. These are snails, shrimp, adn crabs that scavange the tank and "clean" it. They will eat leftover food and help control algee and micro organism growth.
4th) Once cc crew is in, and parameters are ok, begin adding fish slowly. 1 ever few weeks. Always check the water before ordering/purchasing and before adding. I know some people have mentioned QT, that is a option depending on the reliability of where you get your fish from. (The premis of QT is to make sure the live stock is disease free and acclimated to your water, and does not sicken any other fish.)
5th) Everything in saltwater is proportional, rock, sand, watts of lights. Everything has a suggested porportion to the size of your tank. (IE 1 to 1 1/2 lbs of LR per gallon, 4 watts per gallon of light) etc... The point is to get the same type of ratios as the natural ocean.
6th) The lights you have are no where near adaquate for any type of phototropic corals. Stay away from those untill you can upgrade lights.
7th) Before adding anything to your tank. READ, READ, and READ somemore. Don't go squarely off the LFS, they are a business out to make money. Some, not all, but some could care less what works in your tank and what doesnt. They sell you a fish it dies, oh well, you can come back and give them more $ for a new fish. Make sure to check the diet, water conditions, agression, reef safeness, and ability to co exist with other species before adding anything to your tank.
I know all to well the desire to jump right in and and have this big beautiful tank of exotic fish and coral sitting in the living room, but unfortunately, you see the results. I was in the same boat. All I can say is take your time.