The stability problem
Small tanks swing hard. Temperature, pH, and ammonia move faster in 5 gallons than in 20. The single best shrimp tank move is to go bigger than you think you need.
Substrate
Active substrate (Fluval Stratum) for Caridina shrimp that prefer acidic water. Inert substrate for Neocaridina (cherry shrimp), which tolerate a wider pH range.
Filter
Sponge filter. Period. Baby shrimp vanish into any other intake.
Light
Modest. Heavy algae scares off fry; light tanks stay cleaner.
Cycling
Never add shrimp to an uncycled tank. Cycle fully, confirm stable parameters, and add a small test group first. Shrimp sense ammonia long before test kits do.
Plants
Java moss is the shrimp tank standard — it provides grazing surface, hiding places for molts, and shelter for babies. Add some Anubias for visual interest.