Chlorine isn’t safe for small kiddie pools. Although it may sound like a good idea in theory, it’s impossible to get the water-to-chemical proportions right in a small basin that’s prone to water loss from splashing. What’s more, the absence of filters to remove gunk ranging from rogue leaves to skin cells can “distract” disinfectant, tying it up before it can actually go to work on germs. For family-size, semi-permanent pools, follow manufacturer's guidelines on treating the water.