Hello, and welcome to the forum!!

You can add stabilizer via tabs, but it will take a long time. I would just add straight stabilizer--you can get it at WalMart, Home Depot, Lowe's, pools stores, etc. It's often labeled "conditioner", "balancer", or "stabilizer", but look at the ingredient list--if you see cyanuric or isocyanuric acid as the ingredient, that's what you're looking for.

You can either add it through the skimmer, but not backwash/clean your filter for 4-5 days because it takes awhile to dissolve, or you can put it in an old sock and suspend it in front of a return and let it dissolve there.