If you're going to use Trichlor, and there's no reason not to as long as you monitor pH and CYA levels (pH daily, CYA weekly), you should never, ever use ANYTHING but the 99% trichlor tabs.

For every 10ppm of FC, trichlor adds 6ppm of CYA. That's just a fixed ratio of the chemical and the pool store guy doesn't have a clue.