Are you sure its 7 meg/L, and not dKH? If it is meq/L thats almost 20 dKH, which is basically off the charts. What is your calcium? If it really is 7 dKH, that is fine, but if not water changes and time is about the only thing that will help you. There is no chemical additive to bring your alk down. Calcium will bring it down a little but not much. What brand of test kit are you using? I know the Salifert kit doesnt even have a reading as high as 7meq/L, so hopefully you meant dKH, because then you would be fine with a dKH of 7.