1. Add a cup of bleach as soon as you have a 6 inches of water in the pool. Then, add a cup of bleach each evening, till it's full. Test before adding; if the chlorine is dark yellow, skip the dose.

2,3. Re-contamination is not the issue to focus on. The pool is CONSTANTLY being contaminated by algae and bacterial spores. Instead, focus on filling with clear water, replacing the Intex cartridges with Unicel cartridges, and making sure the chlorine never gets low.