My fish looks like its dyeing and i dont know why!!!

Question
I set up a 45gal saltwater tank about six months ago and purchised 45lbs of live rock and 90lbs of live sand. After about a month of cycling it when nitrates were in check, i added some snails, crabs, cucumbers, shrimp, sea urchins, star fish and hermit crabs. They have all been very successfull for the past 5 months so i decided to add two fish, a cardnal and psudochromis. I just added them yesterday they wont eat and the cardnal looks like its going to die because its flopping around at the bottom of the tank, the psudochromis looks fine but is wedging itself inbetween rocks. My Ph is about 8, Nitrates and Nitrites aren't a culperate but my alkilinity is a little too high. I have a protien skimmer, and the tank is kept at 82 degrees. I do regular 8gal water changes every week, and add vitaminmineral suppliments, pro-buffer and amonia detox. I have a hang on the back filter and change one of the two pads every other week. I do get alot of brown algae(I dont know if this could be a sign of something)I am also using well water but it is not really high in any minerals. What is causing my fish to die, could it have just been a bad one from the pet store? Is there anything i can do that will help revive it?

Answer
THERE ARE TWO POSSIBILITIES. YOU MIGHT HAVE PURCHASED SICK FISH OR THERE IS SOMETHING WE ARE NOT THINKING OF. IT SOUNDS LIKE BOTH FISH HAD A TOUGH TIME IN TRANSITION FROM WHERE CAUGHT TO YOUR TANK. YOUR LEVELS AND NUMBERS ALL SOUND GOOD. HOW LONG DO YOU TAKE, AND WHAT METHOD DO YOU USE TO ACCLIMATE YOUR NEW FISH TO YOUR TANK WATER? VERY IMPORTANT. BY THE WAY ALWAYS ASK IF YOUR TO SEE YOUR FISH EAT AT THE STORE BEFORE YOU PURCHASE THEM.