Mustard Algae, 2nd year of battle

For yellow/mustard algae, it likes to grow in shady areas so check under any removable ladders (if the pool were a plaster pool, then I'd have you check behind light niches, but I assume with your vinyl pool that you don't have those). If you don't kill it at its source, it'll come back unless you keep the chlorine at a higher level (around 15% of the CYA level for maintenance; shock level is 60% of the CYA level) which can be impractical as it is more costly.

chem geek, I do have a pool light, but it has never worked since we bought the house. Well, I'm assuming it doesn't work, since I can't figure out how to turn it on. No switch that I can find seems to work it. So, I probably do need to clean behind it.

Mustard algae is back. I still have not done the borax thing, but hope to be able to do it this week.