Whatever you do, you don't want to do it too fast. I think an alk swing would be worse than high alk.
Honestly, I wouldn't do anything yet. Tomorrow see if you can have a friend test your water with something other than api. I used to use api & my alk was always great but nothing was growing in my rank. I got a salifert kit & compared results... My alk was actually only 5.4. I have no faith in api tests. Maybe you're not as high as you're thinking it is. Don't go doing anything drastic yet. You might end up causing more/worse problems.
I think the salt you are thinking of may be Tropic Marin...
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