Hi Hal,
what I've always used is either baking soda or pH-Up in a paste on the green 'sponge' that you mentioned. The pH-Up seems to work a little better (it's sodium carbonate -- the Arm and Hammer washing soda mentioned elswhere on this site). I'm not saying that mneal's nor (and especially) Evan's products aren't great - I've just seen the 'tile and liner' cleaners, from the places I've worked, cause a foaming problem. While the amount of pH-Up or baking soda you need to clean the tile line is small for most pools, it will effect the pH and alk - so may not be a good idea if you're already at the upper level of where you want those values to be. However, you probably already have some baking soda on hand - it's always nice to save a few $

Good luck with your pool's spring cleaning - and let us know how the church's pool is progressing!