The GH/calcium should, theoretically, be fine. You should not need to increase it.
If you purchased adult shrimp, especially if imported shrimp, that could be #1 issue. Number 2, they might be getting too much protein in their diet and need more algae/vegetable based foods. (many "algae" pellets are actually algae infused... with algae being the 5th-9th ingredient) Third idea, maybe not enough oxygen?
Could also try dripping the water back into the tank after doing water changes.