The algae returned while we were out of town. Since I had the filter cartridges cleaned before we left, I'm just going to have to battle it away step by step. Raised the cl level back up with some Zappit and now the algae isn't visible. I'm going to order a test kit today.

My FIL actually came by twice and if I'd known he was going to do that I'd have asked him to dump in some bleach! Next time...