From another site How to raise Rosy Reds, Pimephales promelas, with pictures

In the Aquarium. Our basic setup for breeding this fish in the lab was a 10-gallon aquarium with an under gravel filter. We used 4-inch-long sections of 4-inch diameter PVC pipe for the egglaying sites, two per tank. A new clay flowerpot laid on its side or a slate cave would work as well.
Lighting. Two males and four females went into each breeding tank. Photoperiod (duration of lighting) was 15 hours per day. Temperature was 72 to 74 degrees.
Egg Harvesting. At peak breeding, I was removing one or both tubing sections with eggs weekly and replacing them with fresh ones. The ones with eggs were placed in separate aquaria with aeration and treated with a fungus preventive.
Parental Care. It wouldn’t have mattered to the fry whether they hatched in Papa’s presence or not. Once free-swimming, the fry are ignored by the parents, so long as those parents are kept well-fed.
Increased Eggs. We merely removed the eggs to increase egg production. Once Papa is done with previous responsibilities, he’s ready to go again. Females seem to be egg machines. If the eggs aren’t removed, Papa will clean and protect them until they hatch.