It just depends on the ph. of your soil. Generally speaking, you want to keep your watering ph. at 6.0 to 6.8. the lower figure for vege, and the higher level for bloom. Your soil ph. will tell the final water ph. level you need. If your soil ph. is low, of course you would ad the higher level...
Run off water is not correct, do not trust this. I have the very best soil and npk testers on the market. Both of my ph testers say that my soil is right at 6.0 ph, but the run off says 7.9. My plants are beautiful with no signs of deficiencies and are in the final week of flower. So My opinion...
Leaves curling during flower here too probably from nitrogen toxicity, try a minute amount of aluminum sulfate, seems to work immediately for soil ph reduction!!
If you are using the same amount of amendments as stated earlier it does cost that much! Of course you can cut corners but whos to say what creates the best flavors and aromas.