Caridina Shrimp

Caridina shrimp (Crystal Reds, Taiwan Bees, and their many colour variants) are the species that made "shrimp keeping" its own branch of the hobby. They're also the species most likely to punish you for getting the water wrong. Where Neocaridina are forgiving, Caridina are precise. They need soft, acidic water with almost no carbonate buffering: a GH of 4–6 °dH, a KH near zero, and a pH between 6.0 and 6.8.

The reason is evolutionary. These shrimp come from soft, mineral-poor streams in southern China and Taiwan. Their physiology is adapted to low-mineral conditions, and they can't regulate their internal chemistry efficiently when the surrounding water is too hard or too alkaline. High KH is particularly problematic because it forces pH upward, which interferes with moulting. A shrimp that can't moult dies.

Most serious Caridina keepers use RO water remineralised with a species-specific product. Bottled water blending can achieve the same result if the available waters are soft enough. The key constraint is KH: you need it at or near zero, which means your base water can't have significant bicarbonate content.