Check ph before each watering?

Should we check the ph of the soil before each watering? Will the soil's ph change? (I know this is probably a stupid question...keep in mind I have never grown anything)

YES!!!!!!!....and YES!!!!...optimal range is between 6.0-6.5 depending on strain...some like less. And about once a month flush your plants with 2-3x the amount of water to pot size...(if you have a 2 gallon pot use 4-6 gallons to flush)