10 gallons of 12.5%. Cost, $30, plus deposits on carboys.

Next time you add that much: another $30. That's about $65 already.

The three recommended test kits:
1) PoolDoc's PS-234 (the best and easiest to use)
2) Taylor 2006 (similar, but harder to use)
3) Chlorine FAS-DPD Service Test kit (Leslie's on-line branded version of the 2006)

all cost in that ballpark. Used correctly, each of them will save you getting into a situation where you NEED $65 worth of chlorine in a hurry!

In other words, the GOOD test kit will pay for itself in the first season and keep on paying for itself. You test chlorine and pH every day or two (and the PS-234 has a daily OTO test kit) and you test everything with the full tests once a week. That way you see potential problems before they become problems and compensate ahead of time.

By not having to fix problems, you don't have to use more than the B-B-Bs, muriatic acid and CYA (only once a season, usually), which saves money, time and aggravation. You don't need flocculants, clarifiers, sequestrants, or flux-capacitor magnets guaranteed to empty your wallet.