You never use Trichlor tabs in the skimmer, at least when the pump isn't always running, because when the pump goes off the lack of circulation has the area around the Trichlor tab become very acidic and damaging. Also, the BBB method generally uses chlorinating liquid or bleach as the primary source of chlorine. You would only use Trichlor tabs if you were trying to build up your Cyanuric Acid (CYA) level or were on vacation and needed automatic dosing of chlorine (for up to a week).

Your FC level is too low for your CYA level. You should be following the levels in the Best Guess Chlorine Chart