i have a fire shrimp, when i first got him i turned off my lights, placed the bag in the tank for 3 or so minutes, then put in 5ml of my tank water into the bag every few minutes or so, i only acclimated him for about 10 min or so then let him in. he's doing just great 3 weeks later and has shed his shell twice already.
i just got a clown today and did the same w/ him, he's doing great. he's been putting flakes in his mouth and spitting them out making a mess in tank so im going to try some brine shrimp later tonight.
there must be something major wrong w/ your water. do you have any inverts in your tank? if you have crabs or so and they are doing great then there is no reason why your shrimp should die.
i test my water for ammonia and nitrite every once in a while, and do water changes through out the week. i add some kent dKH
powder stuff, just a tiny pinch of it sometimes, i dont know the levels of calcium or anything or w/e but my coroline is growing crazy and my fish love to eat all the food i put it so i think my tank is fine.
you may want to do what im going to do in the near future, im going to buy a sea urchin, im thinking a pencil urchin, from what i hear, they will loose their spines when the water quality is bad, which will give me time to check things out and fix the water, its a great visual of water quality. the spines grow back, and that warning can pay off if you have expensive live stock.