I suggest that you keep 30-40 gallons of water in the barrel and change it every 10 days as needed. I would suggest that you feed them goldfish flakes that is around 40% protein, you can get it at Walmart. If you are on chlorinated city water then have a second barrel that the water is allowed to sit for several days for the chlorine to escape before exchanging. Further I would suggest you add 1/2 cup of rock salt (ice cream salt) to toughen the minnows, promote slime and assist in killing any infections due to mishandling.