There are a few reasons as to why it may seem as though your Mini may not be working -
First let me explain the types of chlorine, free chlorine, combined chlorine and total chlorine.
Free chlorine is chlorine that is available to combine with contaminates in the water to disinfect and sanitize the water. Free chlorine may also be referred to as residual chlorine.
Combined chlorine is the after is has bonded with contaminants. In this state, it is no longer able to continue its sanitizing effect. It has done its job and must wait for additional chlorine to come in to continue to disinfect the water.
Total chlorine is the total amount of chlorine in the pool, that is, the sum of both the free chlorine and the combined chlorine that holds the dirt, oils and other compounds that make the water dirty.
It is very important that when the Mini is first placed in the spa that the chemicals in the water are balanced. You want your free chlorine (residual) at 2-4 ppm. This ensures that the Mini is not trying to “repair” the water’s condition upon startup.
Two questions to ask:
Did you start your spa with a residual of 2-4 ppm of chlorine?
Are you seeing lots of tiny white bubbles coming off the Mini cell when it’s in the water?
First ensure the mini is making chlorine by placing it in the salt water and looking to see lots of tiny white bubbles coming off the cell, if so, the mini is making chlorine correctly. I recommend shocking the water with some chlorine based shock with stabilizer when first start your Mini. Shocking will give you two benefits to your start up, first, it will kill all the contaminates in the water allowing you to start building a free chlorine residual, second, it will leave a residual of chlorine free chlorine. There may also be some other problems with your water chemistry such as your pH or alkalinity may be out of balance causing your chlorine to oxidize off too quickly. If your spa gets direct sunlight you will need to add some stabilizer to the water to prevent the sun from oxidizing the chlorine too quickly.