The thing about that is they'd be right. 500ppm is at the lower end of adequate while 250ppm is deficient. This is true for ALL stages of growth, including seedlings.
250ppm is borderline starvation, even with a 0.5 scale. Try starting your plants at what you consider full strength and you will see. You're not going to burn seedlings with adequate levels of nutrition. (talking hydro here since soil should already have nutrients build right into the soil). If it won't burn adults, it's not going to burn seedlings, in fact your seedlings wish you'd do this.
