While Flourish Comprehensive is supposed to provide the micros, I've seen a lot of posts with questions regarding issues with combining dry ferts with liquids, so that may be one of the issues.
Also, I can't tell how low those leaves are, or how shaded, and knowing that plants will sometimes cannibalize lower, older, shaded leaves for the higher ones (sacrificing the few for the benefit of the many), *snip*
i vote K def... i'm 99% positive. that plant is the very first aquatic plant that i've owned. incredible K hog. k2so4 in addition to kh2po4 and kno3 and it will turn around. all of the leaves with the holes in them will fall off and you will get plenty of fresh green growth. k is a mobile nutrient. so when there is a lack of k for new leaves the plant robs the old leaves of k and causes those holes.
i dose k on the same day as i dose trace and i dose equal amounts.
When looking for specific deficiencies, and I don't really believe in doing so, always look first at CO2. That is by far the nutrient that plants use the most of, the nutrient that is the hardest to provide an adequate supply of, and the nutrient that is hardest to confirm that you have an adequate supply of. If you can improve that one, and the problem persists, just try doubling the EI recommended dosages to see if that helps. It won't do any harm to try it.
All I can really stand by is my experience with this plant. I had the same problems with it. I dosed more K in response, and it turned around quickly. No more holes, no other problems. It took off and grew with no problems after that.