Isopods or?

[Chaloupa]

HELP! I have a 65g hex with 60lbs live rock, a 3-4 inch live sand base, 1 Frogspawn coral, 2 red bulb anemones, 2 giant feather dusters, 2 Skunk Cleaner shrimp, 1 Coral banded shrimp. All our ALK 10-11, Calcium 325+, pH 8.3, Nitrate 10, Nitrite and Ammonia 0, Temp 80, Remora skimmer, 10g sump with 10lbs live rock, Coralife Aqualight Pro, we water change every 2 weeks and add all our supplements weekly ie Tech A/B etc. Now you know the tank...here's our problem;
got 4 nice clown fish....eat well the first few days, then slowly one by one they stop eating, and 2 days later die....we thought it was because of our ALK and other levels that weren't under control, (we didn't know this until much later), so we tried another 4 clowns...even nicer than the first 4 the same scenario...look great eat well, stop eating and 1 by one they die 2 days later (after stopping eating). So we have had some help getting our levels fixed up (we were very new to the salt water hobby) The levels weren't out of control but not ideal. So all levels now "perfect". We got 6 tank raised Banggai Cardinals. Looked amazing, eating well....same scenario; stop eating and 2 days later they die. OK, this is getting costly. We are completely at our wits end. We have had some suggestions that we have Isopods that came in with our live rock....they suck the blood from the fish and then the fish die. Of course we have never seen any as they feed from the fish at night, and drop off in the light. We have viewed the tank using the moonlights for hours and never seen one. WE NEED HELP! No one seems to know what to do or how to deal with this parasite...IF that is what we have. Any input would be very appreciated! We are ready to take apart the tank and start over. Our next step with the tank is to take out the live sand bed and just put a fine layer of substrate to give the Isopods (again IF that is the problem) less hiding space. Some people have suggested adding a Fairy Wrasse or 6 line.....we are nervous to add them as we have lost enough fish now....other suggestion is to add Lufenuron (Program flea control for cats/dogs) but to remove the shrimps first and possibly the F. Dusters. Our shrimp and other animals are doing excellent. We were also told that if we have Isopods they would also attach to the shrimp and cause them to have the same scenario......HELP HELP HELP! Sarah