I have my first lion fish 4 years ago and suffer the same problem with you, cloudy eye, loss of color and die .
IMO i think the diet is the key part in the success of keeping the lion fish, fresh water shrimp does not give the nutrient that the fish need , and they dont eat this in the wild. I kept my second lion fish in my office for about 2 year feeding it daily with frozen mysis cube each day (soaking it with kent marine Zoe once in awhile), until i sold it away few month ago. I never change my water for about one year, and it is just a simple 2ft setup running with live rocks and redsea skimmer without any sump / overflow. For maintaining the water, I just dose trace elements, iodine and ca one a week.
It is advisable to buy one which is already train to eat frozen food , get the LFS to show it to you if you can or buying it from reefer which has already train it. It is pretty hard to train a lion fish to eat frozen but if you do a search in SRC here, you should be able to find some good information share by some reefer previously how to train it.