I had a gallon of 10 percent algaecide dumped in our12x24x4' pool is it safe to swim in?

The linear quat algaecide that comes in the gallon jugs is a very dilute solution. The quart containers are typically 50% or 60% concentrate....so a gallon of 10% concentrate is roughly equal to adding 1/5 of a quart bottle of concentrate. The linear quats are safe to swim in almost immediately. However, linear quats do cause foaming. That's not a big issue, but many folks don't like that side effect. The better algaecide to use is 60% Polyquat. It comes in quart bottles, and the chemical name on the side of the bottle is a very long name...but it starts with the Word "Poly". Polyquat is more effective, it doesn't foam, and it also acts as a clarifier. It generally costs about $20 for a quart bottle, and the cheapest I've found it is at lesliespool.com and intheswim.com