Definition of precipitate. 1  1 : a substance separated from a solution or suspension by chemical or physical change usually as an insoluble amorphous or crystalline solid. 2  2 : a product, result, or outcome of some process or action.
Oftentimes, replacing a transmission solenoid will take no more than 2 hours, and repair shops on average charge $60 to $100 per hour for labor, not including cost of parts (a replacement solenoid should cost you no more than $200) or shop fees.
Once you determine a schedule that works for you, testing can be done less frequently to confirm your routine is adequate. As a general guideline, you could start with a 20-30% water change once a week. Some people prefer to do a larger change less frequently, such as 40-50% every two weeks. I believe the latter is less desirable since the water chemistry changes more dramatically at once, putting more stress on the fish.