How does pH have anything to do with how strong your nutrient solution is?
The nutrients are absorbed depending on your pH level. If you have a very high EC solution but the pH is not optimal the plants won't absorb as much nutrient. The same high EC with the optimal pH will permit the plant to absorb the nutrient at a much higher level, but you run the risk of running into nutrient burn. Ideally you need an optimal pH and a nutrient solution with an EC just under the level of nute burn. The level of EC can be quite tricky to work out, since for a period of time (i.e. a couple of weeks) your EC can be higher that the level that causes burns without burning the plants, since they are stocking nutrients in the stems, leaves, buds etc. Eventually the plant material becomes saturated with nutrients and if you maintain an EC level as high as you did before the leaves will start burning.

This is for hydro, for soil the same principles apply, but they are harder to control precisely since the soil will buffer against quick variations of the EC or pH level.