The only time you will run into ph problems when your soil is right and your water is right is when you use too much fertilizer too often. It will lead to salt buildups and lower the ph of the soil. It can cause leaves to yellow, claw, and cause necrosis if not treated because the ph is out of range for the nutrients to be taken in by the roots. Low ph will show itself as a deficiency of some sort because of this. The only thing that can prevent this is regular ph testing of soil and runoff, or making sure you have garden lime mixed in with your soil which acts as a buffer. If its a ph problem because of the water being off then it can be fixed by top dressing with lime, if its low ph because of salt buildup flushing is the only solution really. I would say...with what I have come across on here with people claiming ph problems, simply using less nutes and watering with plenty of runoff usually does the trick. If you are using top notch soil made for growing cannabis you will rarely run into problems with ph. Most of the real ph problems are from soil bought at your local store like miracle grow which is acidic to begin with because of all the damn bark and twigs in it.
you should just listen to everything he says 
