Temperature is quite cool, around 27. Most of the shrimp show the same symptoms.. body turn white and die although they might eat normally and etc.. but still die. Then I moved them to a different tank, different substrate and etc. I don't know what is special in this tank, but the white ones eventually recovered and become transparent again. I searched for the condition on the net and it seems that this happens if shrimp don't get enough iodine in their diet. There's iodine supplements and etc available to prevent this. I think algae and etc would contain iodine at least a bit.. so I think it's because the tank before this... no algae.. because quite shaded and no lights..