I have to wonder if the Seachem Advance I am using could be promoting the leaf rooting. From Seachem, the supplement is:
"Natural phytohormone supplement for the planted aquarium that dramatically stimulates the growth of both roots and shoots in aquatic plants"
I have been dosing daily for past 5 weeks.
Ooh, that's kind of wild. I wonder what it is. Don't get me wrong, plant hormones or their synthetic counterparts get applied all the time for many different purposes, but I haven't heard about them being used in the hobby, especially as something intended for end users (as opposed to the the growers who mass produce the plants) and to be used all the time.
I have a lot of questions about this! I wish they said what the hormone is. There aren't that many plant hormones, and they all are involved in many processes and it varies a lot by concentration and different species react differently. My working knowledge of plant hormones is rusty, so I'll have to run their extensive list of involved processes by some old notes and try to guess what they're are playing at.
What I can say is that the concentration of the hormone is low - only 3 ppm in the bottle, so obviously that would be diluted in the tank. What's 5 ml at 3 ppm in 20 gallons? I'm skeptical that's enough to cause much change regardless of what it actually is, but I need to think about it more.
The short answer is sure, that could definitely be a factor, but I don't really know.