Sounds like a plan, wonder if three smaller plants would yield more or less than the two you have in the screen now? Yeah mylar would probably help a bit, though you don't seem to have any hot spots on them. That'd be my first guess, if you have a chance to stop by an aquarium/pet store you can get a pH set (test, up, down) for pretty cheap. Think I got mine for around $8 for all three and should last me at least a few more months. The pH being so low could be locking something out, not sure what it would be to cause that. I'll try to find a chart I saw before that had a bunch of the deficiency and toxicity symptoms and pH availabilities.