The water should contain chlorine in order to kill germs. You won't know who or what might land in your pool.
Reduces alkalinity of swimming pool water (softens hard water)
It is necessary because the chlorine kills all of the germs that enter the swimming pool.
Remove some water in container (10-20%) and add new water. example: pump water high in cyanuric acid out of a swimming pool and the add fresh water to the pool.
You shouldn't add chemicals to a pool in which people are swimming. Add the chemicals, ensure that you've made the correct adjustment to the water chemistry and that the water is safe, and then allow people back in. To be honest, it probably wouldn't hurt them - but it wouldn't be wise.
Drain some water out, a little at a time, and add fresh water.
Add rain water this has very low alkalinity
just add orange juice, watermelon and of course some pig trotters!
It's not possible to add optimizer plus to a pool with the solar cover on. You will need to remove the solar cover from part or all of the pool in order to put optimizer or other pool treatment products into your swimming pool water.
Usually you would add muriatic acid to adjust the pools acid level.
You will need to add an amount of chemicals that is proportional to the size of your pool. The containers of the chemicals should tell you how much to add for the size of pool you have. It might be better if you take a sample of water to a local pool supply store, so that they can tell you exactly what you need for your specific pool. http://www.ehow.com/about_5390392_chemicals-put-new-pool.html
Shock treatment for the green part. If it is still cloudy you can add a clarifier sold at your local pool supply.
You can purchase testing strips which will indicate your pool water's levels of chlorine, pH and so on. With this information, you can determine which chemicals you need to add, and in what amounts. Visit a pool supply store to get the supplies.