1. Yes, add borax, if your pH shows low. But, you might want to set some pool water out in a shallow glass bowl, in the sun, and test the pH at the end of the day. Hopefully, the chlorine will be low enough to get a valid pH reading. Worst case: adding too much borax won't hurt much.

2. Be sure to brush the pool carefully. You don't want to leave any undisturbed piles of algae. Free chlorine does NOT penetrate 'algae clumps' well.

3. Do what you can to help your filter. Or, consider filling to overflow, turning your pump off overnight, and vacuuming to waste (via siphon) in the AM -- to get the settled algae out.

Ben