Crystal Tetra

Protocheirodon pi, the Crystal Tetra, is one of the more unusual and rarely encountered tetras in the aquarium hobby, prized by specialists for its extraordinary translucency. The body is almost entirely transparent, with internal organs dimly visible, and the lateral line region displays a faint but captivating iridescent blue-silver stripe. This ghost-like transparency creates a surreal appearance in a densely planted aquarium, particularly when the fish schools and the stripe shimmers collectively. Found in the soft, acidic blackwater rivers of Brazil's Amazon basin, the Crystal Tetra is adapted to very specific water chemistry — low pH, extremely soft water, and high tannin content. It does not adapt well to hard or alkaline water and will decline in conditions far outside its natural parameters. This species is rarely bred in captivity, and most specimens in the trade are wild-caught, adding to its rarity and appeal among experienced collectors. Its intermediate difficulty rating reflects both its water chemistry requirements and the need for a mature, biologically stable aquarium. It should be housed only with very small, calm, non-competing species and kept in larger schools to reduce shyness.

Tank Setup A 60-liter aquarium is appropriate for a school. Design a blackwater biotope with dark fine-grained substrate, fallen leaves (Indian almond, oak), driftwood, and heavy planting with Java fern, Microsorum, and mosses. Very dim lighting is preferred; floating plants help filter light. Water should be visibly tannin-stained.

Water Parameters Maintain pH 5.0–6.5, temperature 23–27°C, and extremely soft water below 6 GH. These parameters are non-negotiable for long-term health; deviations cause rapid stress and disease susceptibility. Use RO water remineralized lightly, with peat or Indian almond leaves for humic acids. Perform 15–20% weekly water changes with matched chemistry.

Filtration A mature sponge filter is ideal — it provides biological filtration without disturbing the soft substrate or creating problematic current. The tank must be fully cycled and biologically stable before introducing this species. Do not add to new setups.

Diet Feed baby brine shrimp, micro-worms, daphnia, and very fine flake or micro-pellets. Mouth size is small; all foods must be appropriately sized. Feed twice daily in tiny amounts. Overfeeding rapidly degrades water quality in soft acidic setups.

Tankmates Keep only with the smallest, most peaceful species: pencilfish (Nannostomus), other small transparent tetras, dwarf corydoras, or small microrasboras. Avoid any species that may outcompete it for food or cause any form of stress. A species-only tank is also excellent.

Breeding Extremely rarely achieved in captivity. Requires pristine, very soft and acidic water, dim lighting, and live food conditioning. If spawning occurs, eggs and fry are very small and delicate. First food must be infusoria or very fine live cultures. Maintain strict water quality throughout.