Clean the surface to get any slime and loose dirt off. Use a primer that adheres to the type of material that the pool is made of, Killz or Zissner. Then apply the paint color in enough layers to the desired tone. Doing it right takes longer, but it’ll last longer.

The paint in the pool would have stripped regardless without cleaning and priming which I’m guessing they skipped. The hydrogen peroxide just sped things up.