Unlike chlorine, for bromine to be effective there must be a residual bromide bank established in the spa water. The addition of bromine granules or bromine tabs takes time to convert to bromide. Adding a packet of start up after draining and refilling your hot tub creates an immediate bromine level that will show up on a test strip. This acts as a jump start for your hot tub sanitizer until the tablets or granules can become fully effective. Use a packet every time the spa is drained and refilled.