The Pool Frog XL Pro Chlorine Bac Pac 540C comes pre-filled with chlorine and easily inserts into the Pool Frog Chlorine Cycler, dispensing low levels of chlorine for approximately 2-4 weeks. With precise feeding, chlorine lasts 2x longer as you only need a 0.5-1.0 ppm level.Pool Frog is the only mineral system with a pre-filled chlorine pac that meets the EPA requirements to lower previously approved safe chlorine levels by up to 50%.