Read the label, but usually it is safe. Pool Masters
Its never done me any harm. However follow the directions on the container of the algaecide, if it tels you not to swim in the water for a period of time after treatment I would head their advice.
Most 50% algaecides if added properly according to gallons of water in your pool allow you to swim immediatly after adding.
Algecides aren't very harmful to humans or pets but for safety's sake wait an hour for most pool chemicals. If your algecide has copper as the active ingredient, wait a few hours longer just to keep the blonde-haired kids hair from going green.
Shock your pool at sundown and you can swim in it the next morning.
You want to have the equipment running while adding any chemicals. You will want to wait about an hour after adding algaecide.
maybe if you like to hurt yourself
Any time you like calcium is harmless
you should have your pool tested just to be on the safe side.
Adding algaecide to the pool when the filter is on should not do any harm in fact it should mix it into the water more quickly
It will take from days to weeks to have that much algaecide displaced. You should not use the pool during that time. NEXT TIME READ THE INSTRUCTIONS ON THE PRODUCTS THAT YOU USE BEFORE YOU USE IT. I would also watch out for any side effects from the copious amounts of algaecide used.
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
Most metal control products are safe to add with no harm to bathers