H2O2 burn?? I've never heard of that. Something else to research LOL.
Not that I doubt both suggestions, but how could it be PH swing when it's read stable for the last two weeks? The runoff is always the same as the level I pour in...5.8-6.1. Is that enough to be PH swing or am I missing something? I am NOT using calmag yet, but I need to. I just read, especially using distilled water (which I thought would be safer while adding nutes), that calmag is necessary...I was unaware. I'm stopping off and getting some tonight. It's weird though, all the new growth on the problem plant is ok, and it's still flowering nicely. It's jut the current/older leaves that are starting to get all outta whack. But I fear it may be indicative of something else that if I don't catch, could take the whole plant with it.

They are two different strains. The two good plants are one, the bad is another. So one needing different methods than the other doesn't surprise me and it's been something I've been meaning to ask but spaced it.

I will continue to use the same methods for the two good ones, and try to drive the bad one a little differently.

So to recap if I may ask:

-H2O2 burn...what is it?
-Can it be PH swing if it's always between 5.8-6.1, or am I not understanding that correctly?
-Could the lack of calmag be the total issue?
-Is the fact that the new growth looks good now, but the older fan leaves that are affected mean anything??

I forgot to mention I fed them Botanicare Pro Bloom for flowering if that helps.

Thanks again for the replies, you all rock! Hopefully I'll get this figured out.

*junk