The freshwater invertebrate hobby has exploded in the past 15 years, driven by Caridina shrimp grading culture from East Asia. The hobby now supports dozens of distinct grade lineages (CRS SSS, Crystal Black, Black King Kong, Mosura Pinto, Galaxy Fishbone, Wine Red, Blue Bolt) that command three-figure prices for high-grade specimens. Neocaridina (cherry shrimp variants - red, yellow, blue dream, blue velvet, black, green jade) provide the entry-level on-ramp at $3-15/specimen.
Beyond shrimp, the FW invert category includes nerite snails (zebra, horned, tiger, red racer - excellent algae eaters that don't reproduce in freshwater), mystery snails (the breeder), assassin snails (eat other snails), bamboo shrimp (filter-feeders - need particulates in the water column), vampire shrimp (rare and visually stunning), amano shrimp (the standard algae shrimp), and crayfish (CPO/orange dwarf, blue, white, electric blue).
Caridina vs Neocaridina is the first decision. Caridina (CRS, Taiwan Bee, Pinto) need soft acidic water (TDS 100-150, GH 4-6, KH 0-1, pH 5.5-6.5) achieved by RO/DI water remineralized with a shrimp-specific mineralizer. Neocaridina prefer harder water (TDS 200-300, GH 8-10, KH 3-6, pH 7.0-7.8). Mixing the two species in the same tank produces stress and reduced reproduction in both populations.
Cherry shrimp (Neocaridina davidi). They breed in stable conditions without intervention, tolerate a wide pH/GH range, and provide a self-sustaining colony for any low-bioload tank.
Most fish will eat shrimp larvae and adults under 1/4 inch. Compatible: otocinclus, dwarf corydoras (pygmaeus, hastatus), small tetras (ember, neon), pencilfish. Generally incompatible: most cichlids, tetras larger than ember, gouramis, bettas, anything that fits a shrimp in its mouth.
Top causes: copper contamination (from medications, plant fertilizers, brass fittings), ammonia spike (often from overfeeding), KH crash (active soils buffer pH down over time), or a temperature/water-change shock during a molt cycle.