Welcome to our forum.
My tap water is relatively high in ALK, but pretty close on for PH. I use PH decreaser to get the alk down, then re test and adjust PH up if necessary.
Does your dealer offer water analysis? I usually take a sample of untreated spa water in and have them do a readout- tells me how much of what chemical I'll need to add to get the water balanced. I have to use a lot of PH decrease to get in range.
I have to add about 24+ ounces of PH decrease whenever I replace my spa water.
I get my Ph increase and Ph decrease from a big box store. For about the same price as I pay for a small container (20 ounces?) at my spa dealer, I can get a much larger quantity, and the ingredients are identical.