yes and no. Definately less than others believe. Checking pH probably let's u get the most of your Nutes. U can wait to change your rez to when the buffer has been used up, or you can add pH down to continue with the same nutes after that. EC should give you an indication if your solution is too strong. If you keep the water topped off everyday and your EC is rising than your solution is too strong. If it falls everyday it is either too weak or just about right.

That's the whole game. Haven't been able to substantiate anything else.