It depend on a lot of things. First of all, if you have a heated pool, you need to give a lot more attention to chemicals as the green things gets comfy very quickly once above about 25⁰C.
I run my pool on 31⁰C.
The most important things to test, are the following:
1. Alcalinity. This MUST be correct in order to provide a buffer for PH changes. To low alcalinity can make PH change quickly under certain weather conditions.
2. PH. If this is not correct, the chlorine cannot do the work properly.
I went for the saltbath system as I find the water to be a lot more pleasing on the skin and it help that I do not need to add chlorine manually every day or when I am away for a few days.
If PH and alcalinity is fine and the chlorinator works as it should, I test my water weekly with those simple test strips with the squares on. It works good enough.
Be very very cautious for adding stabiliser. Once in the water, it cannot get out because of evaporation hence adding water for makeup is no reason to add stabiliser. It works, but if over stabilised, the chlorine cannot work. Thus, you will test high chlorine but cannot understand why the pool is green.
Water? Add as needed. More in summer, less in winter.