He told you to monitor the water / nutrient solution pH and run off pH to ensure that the run off pH does not exceed 6.1 pH...
Ideally aim for 5.8 / 6.0 pH, and your run off should be the same, if it gets lower or higher then you need to boost it up to get the correct pH balance back (avoiding lock out issues).
Keep your pH in check, the rest is down to lighting and personal ability.