If the water in your kiddie pool looks green, chances are that algae is the culprit. In large amounts, algae is unattractive, slippery and unsanitary. When untreated water is left to stand in your pool over a few days, algae will inevitably develop. If your pool is small enough, you can dump out and refill the water every day to prevent algae buildup. For larger pools you will need to use an algaecide treatment.
Make a paste of baking soda and water.
Drain your pool and use the solution and a pool brush to scrub algae from the bottom and sides of your pool. Rinse the pool thoroughly.
Fill the pool again with water. If your pool is too large to drain more often than once a week, use a combination of chlorine and algaecide to prevent algae buildup.
Calculate the amounts of chemicals you will need for your pool using a calculation method such as that provided at the website Pool Solutions (see Resources).
Add the proper amount of bleach and borax. Wait an hour.
Test your pool. If the chlorine level is under 3.0 or if the pH level is under 7.4, add another dose of bleach and borax.
Add the proper amount of algaecide.
Test your pool again before using it. If the chlorine is under 2.0, dissolve a dose of chlorinating concentrate and wait 10 minutes before retesting.
Drain your pool every week and repeat this process unless you have a pump and filter.