If they are chlorine tabs it is either Tri-Chlor or Calcium-based, as Di-Chlor cannot be tabletized. I thoroughly recommend *against* chlorine tablets as they create a gas build-up that is not only noxious and hazardous to your health, it also chews away at the underside of your cover, allowing it to take on water faster and causing it to be replaced sooner. Additionally- Tri-Chlors will lower your pH faster and more frequently.
I'd switch to granulated Di-Chlor if you're going the chlorine route. The first 4 months of water chemistry is the hardest (your water tends to last 4 months before you need to drain it). If you're always running low on chlorine, you're simply not adding enough. Test 3-5x/week if you're trying to establish how much chlorine you need. Once you get your equilibrium, you can throttle down to 1-3x/week for testing, based upon how often you use it.
Remember: Test prior to entering tub, and add chlorine after you get out. Next time you test, if you're low, you added too little and up your dosage (and vice versa).
I hope this helps. Good luck moving forward.