Why swimming pool water have chlorine?

Your chlorine level depends on how often the pool is used, and the time of year. When swimming is at it's peak, the chlorine has to work harder for the pool to be kept clean, and when it's warmer, the chance for algae to grow is much greater. Buy a pool test kit and check your levels periodically. check daily at first, and then you will get an idea of your pool usage, and when to add chlorine. I had a pool that had an automatic chlorinator, that used tablets to keep a constant level of chlorine

First you need a pool service company to come out and check out your water. Or, you can take a sample of your water to a pool company and have them check it. Go from there. Make sure this company has been in business for at least 20 years or more. Make sure you pick a company that can accommodate all your needs when it comes to a pool.

I've been using chlorine bleach as a shock treatment for years - never had any ammonia issues. If you have also used any of the algae treatments (Mustard Master, yellow Out, etc.) that could well be the reason for the ammonia. That stuff probably reacted with the chlorine. Chlorine bleach is no different in its cleaning properties than trichlor or HTH. It just isn't stabilized.

You would probably not have amonia problems unless someone war peeing in the pool. Test the water and adjust chems once or twice per week.

use a conditioner and stabilizer to keep chlorine from prematurely dissipating

You need Tri-Chlor chlorine tabs that have cyanuric acid. This is the stabilizer for chlorine. Go to the pool link below for a chart.

Good luck

Robert