This convenient and effective spa start-up hot tub shock comes in an easy to pour packet, with a unique effervescent feature so you know its working. Its bubbling action properly shocks your hot tub water and sets the initial chlorine level on freshly filled spas upto 500 gal; and for SPA FROG Mineral System users, it helps extend the life of your bromine cartridges. Simply open and pour the hot tub shock package into your spa when starting up a freshly filled hot tub (approximately every 4 months). Not currently using the SPA FROG Fresh Mineral Water System to take care of your hot tub? Learn how you can use less chlorine and bromine while still enjoying softer crystal clear water, with no faded swimsuits or smelly odors. SPA FROG® Floating System. SPA FROG® In-Line Hot Tub System.