1. Cardinal Tetras (Paracheirodon axelrodi): These small, vibrant schooling fish add color and movement to the aquarium without posing a threat to discus.
2. Rummy Nose Tetras (Hemigrammus bleheri): Another peaceful schooling species, Rummy Nose Tetras are hardy and can adapt well to the same water parameters as discus.
3. Neon Tetras (Paracheirodon innesi): Similar to Cardinal Tetras, Neon Tetras are popular choices for their bright coloration and peaceful temperament.
4. Glowlight Tetras (Hemigrammus erythrozonus): These beautiful tetras are known for their striking red and black markings and can thrive in discus-friendly water conditions.
5. Hatchetfish (Gasteropelecus spp.): Hatchetfish have an unusual body shape and prefer the upper water levels of the tank, making them interesting but non-intrusive tankmates for discus.
6. Corydoras Catfish (Corydoras spp.): Many species of Corydoras, such as Peppered Corydoras and Bronze Corydoras, are ideal bottom-feeders that won't bother discus and help maintain the cleanliness of the tank.
7. Apistogramma Dwarf Cichlids (Apistogramma spp.): Some species of Apistogramma, such as the Cockatoo Dwarf Cichlid and the Borellii Dwarf Cichlid, are peaceful and small enough not to pose a threat to discus while adding color and variety to the tank.
8. Otocinclus Catfish (Otocinclus spp.): These small catfish are excellent algae eaters and can help keep the tank free from unwanted plant growth.
9. Kuhli Loaches (Pangio kuhlii): Kuhli Loaches are peaceful, eel-like fish that are active during the night. They occupy the bottom levels of the tank and are unlikely to disturb discus.
10. Angels (Pterophyllum scalare): While Angels can sometimes be aggressive, they can coexist with discus if introduced at the same time and provided with plenty of space and hiding places.
It's essential to thoroughly research and understand the specific water parameters, behavior, and size compatibility of each species before introducing them to the discus tank. Additionally, always quarantine new fish before introducing them to the main tank to avoid introducing diseases.