I do 150. I'm not mad-scientist about it--adding drops of tap water, measuring the PPM change until I get exactly 150. But, I try to be close. Say, 135-165.Yeah it took very little ph down like 3 drops in a gallon. Yeah 240ppm was just ro and tap water no nutes this watering, i feed nutes every other watering. So 200-250ppm is too high iyo? I though you wanted a base water at about that ppm before adding your nutes?
I don't do water-only feedings. I believe people feed/water/feed to let the soil biology recover from synthetic nutrients. If I did that, I would add so-called inoculates to the water. (Myco? a tea? I'm not as familiar with these things as I'd like to be.). Without stuff like that, I don't see any reason to do strong/zero/strong nutrients. I think it's preferrable to spread those nutrients across each watering, affect the soil microbes less all the time instead of more/none/more. But, maybe I'm wrong and there's a reason to do it the way people do. You might try spreading the nutrients across each watering and see how it compares, if you haven't before.
I don't know if 200-250ppm would be different than 150. I know GH Flora 3-part is designed for 200 or less. If a user has > 200, GH recommends a "hard water" version of their Micro product. 150 is recommended by one of the "how to" authors. Rosenthal I think.