Amazon community — 200L

Why this setup works

This is the aquarium that turned a generation of hobbyists from casual to obsessed. Cardinals and rummy-nose schooling together in a large planted tank, angelfish hanging in the midwater like living ornaments, corydoras working the substrate below. It is difficult to watch for more than five minutes without revising your plans for the next tank.

The challenge is that this combination has a tension built into it: angelfish and cardinals are from the same rivers in the wild, but in an aquarium the relationship tilts toward predation once the angelfish grow beyond about 8cm. Cardinals are too large to swallow for most of the angelfish's adult life, but the risk at juvenile cardinal size is real. Add large or adult cardinals. Keep the angelfish pair — two adult angelfish in 200L is the sustainable limit before territorial pressure becomes a maintenance problem.

Rummy-nose tetras are one of the best early-warning indicators in a freshwater tank. Their nose flush from red to white under stress or water quality decline before most other species show obvious symptoms. A fading nose is your prompt to test the water and investigate.

Water parameters matter more for this combination than most: temperature 26–28°C, pH 5.5–6.8, very soft if you can manage it. Angelfish are more forgiving about hardness than cardinals, but both want warm, soft water. A RO blend or naturally soft source water is the path of least resistance.

The bristlenose is there for algae control and does the job without competing with the corydoras for food — bristlenose graze wood and glass, corydoras scavenge the substrate. They occupy different spaces and leave each other alone. One bristlenose is enough in 200L.