Hi Matt;
  • Your chlorine from Leslies is 73% strength cal hypo -- it's good stuff for this purpose.
  • You do NOT need to test your filter with DE; it's been catching algae, so it's working fine.
  • You will improve your kill by BRUSHING all the areas where algae has appeared, even if you can't see algae there now.
  • You should brush in the evenings AFTER adding chlorine.
  • If you will raise borates in your pool to around 60 ppm, your pool will be more resistant to this type of algae.
  • BUT, borates are something in addition, not a replacement for chlorine.

It's much easier to answer your questions, when we have the details about your pool in one place. We often 'waste' the first few posts back and forth collecting information. So, please complete our new Pool Chart form -- it takes about 30 seconds, but will save much more than that.
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If you are interested in the borate thing, you'll need about 20 boxes of 20 Mule Team borax, and about 6 gallons of acid - maybe $150. Don't do this if your pool is leaking, or if you are planning to drain it anytime soon. And, ask before you start. There are some other things to do.