Safe for horses and other livestock, our specially formulated Healthy Ponds Stock Tank Pond Water Cleaner treats stock tanks of any size up to 300 gallons for up to 30 days. The dispenser ships with 2 bacteria packets, which will treat a stock tank up to 60 days. For best results, always start with a clean stock tank. The Stock Tank Water Cleaner is veterinarian approved and is completely safe for horses, cattle, and other livestock. Multiple Stock Tank Water Cleaner dispensers will be necessary if more than 300 gallons of water are used per day. Remember to replace the bacteria refill packet every 30 days by replaceing the used packet with a new refill packet.