My first suggestion is for you to stop using the trichlor tabs. They are stabilized which means they have CYA in them. Your CYA is already plenty high. You actually should be keeping your chlorine higher than 4ppm. Take a look at the Best Guess Chlorine Chart in my signature below. With a CYA of 80, your chlorine should be between 5 to 10 ALL the time or you risk an algae bloom.

Regarding raising the alk, it is probably going to take around 7 lbs. of baking soda but you do NOT want to add that much of anything all at one time! Add a lb. at a time slowly to the skimmer while the pump is running. Wait at least 2 or 3 hours or longer, retest and redose until you get the alk somewhere around 100. Take your time. You don't want to cloud your water.

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