So I bought an above ground pool, and taking care of it is something that would be cool to automate.
Not cleaning it, but maintaining chemical balance.
I would need to have submerged chemical sensors:http://www.troublefreepool.com/pool-school/pool_water_chemistry
FC - Free Chlorine - A sanitizer which keeps your pool water safe and free of germs. Chlorine must be constantly replenished.
pH - Acidity/Alkalinity - Needs to be kept in balance to prevent irritation and protect the pool equipment.
TA - Total Alkalinity - Appropriate levels help keep the pH in balance. High levels can cause pH to rise.
CH - Calcium Hardness - Appropriate levels help prevent plaster damage. High levels can cause calcium scaling.
CYA - Cyanuric Acid - Protects chlorine from sunlight and determines the required FC level.
Then based on the results of some math, I would need to dispense certain chemicals. Chemicals can come in either powder form or liquid form. Probably easier to dispense liquid form.