So far I've probably grown about 8 different auto strains using them. In veg I've not been able to get over about 2 ml per gallon with most only being able to handle 1.5 ml. In flower I've pushed a couple up to 3 ml but most seem to do best with 2 ml. I've got some photo plants going at the moment at 6 weeks, two sativas and two indicas. Just put the sativas into flower a couple days ago. Got a bit of nute burn on them at 2 ml so had to back off. The indicas handled the 2 ml just fine.
I do have a few issues with my rain water. The pH and ppm vary quite a bit, ranging from about 8 to 10 on the pH and 40 to 120 on the ppm. When the pH and ppm get that high the low doses don't always bring the pH as low as I'd like. I've explored a couple other sources, my neighbors well, my tap and some spring water, all of which are worse than my rain water. Within the next few months I should have an RO setup going, which will solve that problem.