At the most basic level, you should find kits that can test your total chlorine, free chlorine, pH level, total alkalinity, Cyanuric acid, and calcium hardness. Some test kits may test less than this, while some may test more. Depending on the size of your pool, and the usage, you could go in either direction. If you want to go all out, then a high-end photometric kit will take care of the most expensive swimming surface.