It's a yellow ball called SolarPill.

Also, I have some of this "No Mor Muriatic Acid" powder that the pool store finally sold me. Supposedly, it's "great for salt water systems!". Anyway, I'm out of muriatic acid right now and wondered if I can dissolve it to try one more soak of our salt cell. The instructions say 2.5 lbs = 1 gal of muriatic acid. If this will work, I think I can use 1 lb as an equivalency to 0.4 gals of muriatic acid and add at least 1.6 gals of water to the bucket. Won't try unless you guys give me the go-ahead. Again, the pool store suggested I use this product, but that was at the same time they said to use vinegar. When I asked how much to use, I was told, "Oh, one or two capfuls will be fine in a 5 gal bucket." I can't find any logic in that math.

What are your thoughts?