The first thing that I notice is that your chlorine level is too low for a CYA reading of 75. Please read the Best Guess Chlorine Chart in my signature below for the connection between CYA and needed chlorine levels.

Your pH is ok at 7.2 but if it goes any lower, you'll want to add some 20 Mule Team Borax (laundry aisle at Walmart).

You should check chlorine and pH daily, alk and calcium every couple of weeks. CYA doesn't need to be checked very often at all unless you use a product that is stabilized (which means that is has CYA in it). And, with a CYA of 75, you don't want to add more.

Hope this helps.