CV-600 and CV-700 enzymes can be added to a pool without downtime.
You can swim immediately when using CV-600/700 enzymes. In fact, people can swim while you add the products.
From a safety perspective, you can use CV-600/700 enzymes without any downtime at all, but with the initial purge dose, the pool is likely to have bubbles. We recommend purging overnight and giving the enzymes time to address the hydrocarbons and other non-living organics in the water. There is no safety risk to swimming during this time, but the water may look ugly and feel soapy during this time. Give it 12 hours and most of the bubbles should be gone.
CV-600 and CV-700 enzymes are both NSF/ANSI Standard 50 Certified, meaning when used as directed, they are both nontoxic and nonhazardous. They used to be NSF/ANSI Standard 60 Certified too (NSF-60 is the drinking water safety standard), but we decided to let that certification lapse. We have not changed our formula, however, so it is the same product in the bottle.
A pool during the initial purge dose. The bubbles are harmless but may make people skeptical of getting in the water. It's okay, it's just carbon dioxide leaving the water thanks to the enzymes doing their job.