The white line you see is calcium build up, the calcium is leached from the plaster into the pool. This can be controlled by watching your alkalinity level in your water and maintaining proper chemical balance.
There are chemicals that are available that will force all dirt suspended in the water to sink to the bottom. To clean the bottom of the pool you can use your polaris or creepy crawler to sweep up. The debris that floats on the top may be removed with a net.
Algae can enter your swimming pool through wind, rain or everyday use of your swimming pool.
If your pool water is not balanced properly, it can lead to skin and eye irritation, it can also harm your equipment and the surface of your pool.
This usually occurs after a super-chlorination of the pool. If this does not go away and you see deposits of white powder material it is probably calcium.
There are several different types of algae, the most common are green, yellow, and black. Green algae is the most common kind found in swimming pools. This algae float in your pool or stick to the walls giving your pool a greenish tint. Yellow algae or also called mustard algae will stick mainly to the walls of the pool. This algae is difficult to remove and often returns. Black algae is the hardest to deal with. It often appears in dark black, green or blue spots. These spots of algae are small, no bigger than a dime. This algae has roots and you must remove them in it entirety or it will return.
Yes, if you have an existing crack and you have your pool re-plastered there is a strong possibility that the crack will return. Depending the type of crack that you have it may be necessary to have epoxy injections done to the cracks.