We've had pretty good luck this summer with a number of "steps".
1) Marigolds. Wasps aren't fond of the smell. A couple of marigold pots near the steps or ladder help a bit.
2)
These wasp traps have worked exceptionally well for us, using apple cider as the bait. We've found them at Aldi for half the price shown on that page.
3) Drowning them.
Wasps can't swim, and are surprisingly prone to drowning. Just splashing them with water from the pool a couple of quick times tends to knock them deep enough into the water they can't fly out. "Escort" them over to the nearest skimmer, viola. You'll also find that they don't seem to take being splashed by water as an aggressive act. I've not yet had one turn on us or the kids (and believe me...I'm attentive to it, as I and the wife are both allergic), but instead they simply fly away if they escape the splash.
4) Bleach water. We keep a pressurized spray pump (Bought at Big Lots for $2) filled with a 50% mixture of bleach and water. It knocks them off of stairs, handrails, etc, and down into the water (see #3 above) without introducing anything scary to the pool. If you have a wood deck, might want to check for discoloration if you're concerned about such things.
It takes a while, and you need to be pretty diligent about going after them when they're there, and changing the traps and such, but all these steps work surprisingly well. it even appears, at our pool at least, to have "sunk in", and reduced the number we're seeing overall.
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As for the borates, you can view
this thread to answer your questions.