good, watching the new growth is the key here....the older stuff won't get any better at all so don't go by that. Keep an eye on your ppms and see if they rise, go down, or stay the same.

You can flush out your system between res changes. It's always a good idea (although I don't do it.....shhhh) but make sure your water if ph'd to the correct level before putting it in your rez. Anything that goes into your rez should be at the proper ph, no matter what.

How are they growing in general? Fast? Slow? Sideways?