I disagree with some comments here. With only 2100 gallons, you can drain and refill several times before paying for the tf100. The FC and ph kit you have is fine. If you've added one tab so far, your cya level is around 15. Add one more, then switch to bleach. Assume you have a cya level of 30 at that point.
Test using your drop kit. If your test shows any color, go swimming. If its clear add 3 cups bleach. Maintain your ph as suggested in pool school. The puck you've added brought your FC level to around 23, which is one reason you've had no problems to date.
If it ever goes green.....drain and add two more pucks.