Caridina cantonensis (Crystal Red, Crystal Black, Taiwan Bee, King Kong, Wine Red) needs soft, acidic water with very specific parameters: GH 4-6, KH 0-1, pH 5.8-6.5, TDS 100-150, temperature 68-75F. Tap water rarely hits any of these targets, so Caridina keepers run RO/DI plus active substrate (ADA Amazonia, Brightwell Shrimp Substrate, or Fluval Stratum) which actively buffers the water down to the right pH and KH. Get the setup wrong and the shrimp do not breed; get it right and they breed steadily.
A 10-20 gallon tank, RO/DI water remineralized with Salty Shrimp Bee Shrimp Mineral GH+ to 120 ppm TDS, active substrate at 2-3 inches deep, sponge filter only, moss and almond leaves for cover. No fish. No co-inhabitants other than tiny snails like Pomacea or Neritina if you must. Cycle for at least 4-6 weeks before adding shrimp - active substrate releases ammonia for the first month and shrimp added too early die in waves.
Crystal Reds are graded from C (lowest) up through B, A, S, SS, and SSS. Grade is based on red intensity, white opacity (calcium-rich solid white versus thin translucent white), and pattern symmetry. SS and SSS grade shrimp have thick, calcium-white bands that look almost painted on. Breeding two SS-grade parents produces about 50% SS offspring, 30% A grade, and 20% B grade or lower - even with strong genetics, expression varies. Cull aggressively for the first three generations.
Mischling is German for "mixed breed" and refers to first-generation Crystal Red x Taiwan Bee crosses. Taiwan Bees (Black King Kong, Red King Kong, Wine Red, Panda) bring intense pigmentation to Crystal Red lines. Mischling F1 offspring look like normal Crystal Reds but carry the Taiwan Bee pattern as a recessive trait. Breeding F1 Mischling x F1 Mischling produces about 25% Taiwan Bee patterns in the F2 generation. This is how most modern Taiwan Bees are produced - direct Taiwan Bee pairs are far less productive than Mischling crosses.
If your colony stops producing, the parameter most likely to have drifted is TDS (climbs over time as you top off with low-TDS water without monitoring). Other suspects: KH crept above 1, temperature spiked above 78F, you accidentally introduced trace copper through tap-water top-offs or new equipment. Test TDS weekly, do small water changes (10% per week) with fresh remineralized RO/DI, and avoid aggressive parameter shifts. Caridina respond to stability the way most livestock does - more than they respond to perfection.