I’ve been buying pond comets from the feeder tanks at pet stores for years. Because they can grow to be almost as large as koi, I only keep them for a year or two, depending on how quickly they grow. When they reach a point of becoming too large for my tank, I release them into a pond, where they can grow to their full potential.
My favorite pond for this is the beautiful koi and comet pond at the Green-Wood Cemetery, which is very near my house. Anyway, I did this drawing of the newest member in my small fish tank menagerie (which includes 3 neon tetras and a zebra neon). He is currently about the same size as the neon tetras— so tiny!