adding chemicals such as ph
up are not going to fix the problem. It will also kill tank inhabitants if you do it after you have fish etc in the tank. Ph should be raised quite slowly, over days, not hours or minutes. Are you using ro
water in your salt mix? If not, it may be that the water source is exceptionally low in ph
and the salt mix does not have enough buffer in it to compensate. Incidently, what is the salt mix?