Salt water tank problems

Question
Started my tank about a month ago.  went through trials and tribulations and finally got everything perfect.  (per Local fish store). Fed the fish - all doing great - active, eatng and healthy. Came home from work 1/2 the fish dead and by bedtime the rest of the fish dead.  Eel, lobster,starfish, shrimp, hermit crabs all fine. the only fish to survive is a cleaner rasp.  As they were dying their eyes got cloudy and a white milky coating appeared on them (kind of like their skin was coming off).  What in the world could it be?  All necessary levels of water were good. tempature was 78 degrees.  the fish that died were, clown fish, african clown fish, yellow tang, butterfly, and others that i dont know the name of.  Anything other than a fish survived.  Bubble tipped Anenome seems to be ok. I have coral & lava rock in the tank.  third time I am losing my fish in this mysterious way.  Local fish store is telling my water is perfect and cannot understand.  Warned against using Windex on front of tank which I was using but cant imagine would have been strong enough to kill everything in the tank. Feeding them brine shrimp & krill. using 2 undergravel filters with power heads (no electric is getting in the tank) and 2 hang on bio filters.  any info you can provide is appreciated.  I am going broke and get so upset each time this happens to the poor fish. Thank you, Peter

Answer
Peter,  I am going to give you the quick basics of setting up a new salt tank. This NEVER has to happen. I have found they are much more stable system's and the fish are much hardier and longer lived and alot more personality then fresh. The first thing you do is get either live sand or crushed coral or my fav puca shell not crushed. Get your specs. correct pH, sg, temp. I do not know the size of your tank but, for that many fish assuming the petshop knows what they are talking about for that many it better be at least 125 gallons. The one inch per gallon does not apply to salt fish. You tank should have been cycled out for about four week's with live bacteria (cheap) called cycle prior to adding fish. Also, depending on the size tank you have If it is 125 or more you should have canister filter's on them not back filters. Personally, it sounds like your tank crashed. You should always add your fish maybe one a week  with the larger ones. It sounds like you had a major ammonia spike an it ate your fish. So sad. Do not get discouraged it is not Your fault. If you want to fix this. I need to know the size of your tank and we will stock it correctly. I also would like to know how many powerheads and are they 10's 20's or what and the exact filtration. I am so sorry you are going through this it is so unnecessary if done correctly. No, you are not supposed to use Windex but, I have too. Spraying on the rag first. There are many natural products out there now get that instead. It was not the Windex or everything would be dead. This sounds like a case of overstocking maybe and probably stocking too fast. Hope to here from you soon, Tina