Quote Originally Posted by polishpollack
Don't try to fight the pH too much. You'll never win. What you're using to lower it loses strength after a while. Why people think they need to be in the 5's I'll never understand. As long as the plant looks good, don't worry. Just consider using a higher PPM as the plant grows, if necessary.
Please, please, please, ignore this advice. I'm sorry, Polish, but you couldn't be more wrong.

Having correct pH in a hydro system is CRITICAL to keeping your plants healthy. You need to figure out what's buffering your pH (making it so hard to get it to go down). What type of water and nutes are you using? What's your TDS/PPM at right now? What's the grow medium? How does your reservoir smell? How do your roots look?

Hmmmm....think that about covers the key questions, at least what I can think of for now.