Molting I think. So you should do some checking at the lfs when they do your test get the actual numbers of these things and then buy a GH/KH kit. If you want to keep shrimp, it is a really handy test to have.
Foods with more calcium and minerals, shrimp king has Mineral "food". And there are many others with excellent mineral content.
Sometimes too hard of water or water with too high of TDS can cause it to be harder for the shrimp to molt.
You can also look on your water company provider and see their usually, yearly water quality report and see what the normal water range is. I called mine on time and they checked the monthly report they do and told me the minerals listed.
If it the water report information falls in that water parameters for Cherry shrimp, then you will be okay for that, but I would make a point to do very small water changes, like 5% per day for a week, then 5% either 2x per day like am and pm. or 10% if they look like they are perking up somewhat. For another week and maybe even another week. The reason is that changing such a small amount of water really doesn't turn the total volume of water around very quickly.
Use distilled or RO /DI or RO for the volume of daily evaporated water to refill.
This will help keep things on target.
Water volume changing and frequency of changing in a shrimp tank is a hot topic and many people say only very small pwc's.
In the real world it doesn't matter what I do to my tank, if your water is different, and the shrimp you have were raised, over seas, in another county, or across town in different water parameters than mine.
If someone has dialed in the shrimp to be breeding for them, and that is where your shrimp have come from, try using the water in a parameter that they used/ the shrimp were raised in.
You can use a remineralizer and RO/DI or RO water to get the "perfect" water.
It is a bit more cost, and an extra step or 2 but worth it if your "tap" water isn't the right combination for the shrimp.
