What I meant was how do you tell the difference between pH lockout and a nutrient problem? If the solution is to flush and the plants look better, how do you know that it wasn't a matter of being over fertilized? That would cause the pH problem as fert content in soil or water is what causes the pH to be what it is. pH being one way to the other is dependent on the fert content in the soil. Get that right and you won't have to worry about pH. After 12 weeks of grow time, your plant is small due to weak lighting. The yellowing is from 5 weeks of flower. These plants die naturally and after so many weeks of flower, complicated by weak lighting, it is dying naturally. I suspect that unless you have really screwed up a fert regimen, the last thing you should worry about is pH. Don't mean to sound like a jerk and I know that people are very much into this pH idea, but pH is a symptom of something else going on in the soil or water in hydro. The point is to find the cause of bad pH, which is usually a wrong fert content. Both potting soil and water will have a pretty neutral pH until fert is added, either at a manufacturer or by the grower.
Aren't the high phosphorus bud blaster actually suppose to be given in the first week of flower and only once? What good would it do to give so much phosphorus at the end of the grow? You don't want to load the plant with fert just before harvest. You want to give nothing but water to get the fert out, otherwise you end up consuming those chemicals. No good.