No, get it pH'd to that level first, give it 24hrs, see what it bounces to. That's your goal right now, see how much pH adjuster you need without making huge adjustments while it's active in the system. Use a smaller container and calculate up if necessary, but in my experience with fish, you're gonna kill 'em if you expose them to a pH of 4 and then expose them to the even harsher conditions of pH ranging. That's with fish, and while I think plants may be able to tolerate that a little better, I know that it'll kill vertebrate fish within hours, inverts in less time.
Get a 5gal bucket to play around with this adjustment stuff first, k? The other thing about it is that you won't be using up huge volumes of water trying to get a better feel for this, and you'll also not use up huge volumes of pH adjuster. Try it with vinegar first if you like, but citric acid also works very well IME.
Don't forget also that saturation levels of gasses like oxygen and carbon dioxide directly affect water pH, so aerate for that 24hrs, especially if (since?) the system's constantly circulating.