Tile is placed around the perimeter of the pool because it is a surface that can be easily cleaned. There are many tile cleanser products available which are applied with a scrubbing pad or brush. Remember to never use abrasive cleaners on a vinyl pool.
You can also try to frequently clean the inside of the skimmer. You can also use an enzyme product such as Natural Chemistry’s Pool Perfect Klear that eliminates oil, lotions and organics in pool and hot tub water.