Most of the over the counter soil testers are shit and don't read accurately. I have yet to see one work even decently. If you have one of those, you may not be as bad off as you think you are. Get the soil professional checked at your local garden co-op thru the county. So, don't make a radical change cause you could be making these worse. I'd add some dolomitic lime...... which raises AND lowers ph towards neutral.
Most mediums go acidic (below 7.0) over time, not alkaline (above 7.0) like yours. Fertilizer is a salt and is naturally acidic. Unless your water has a high natural pH or your medium has a naturally high pH from additives, I suspect something else is going on, if you are having problems. If the plants are healthy, and you are worrying about what your think is a high pH, stopped worrying and leave them alone. You're close to flushing now anyway....
