I have probably a few hundred trumpet snails in my big tank. There's probably about 15 or so of them on my monte carlo carpet right now. I've never seen them munch on anything besides dead stuff and algae.
I know you've gotten a few opinions on what might be causing this damage to your plants, so I'll give you mine. It looks exactly like my problems with micro tox I had a year ago. The specifics can be found in the micro tox thread. Running around and trying to blame this on K+ was the first step of my denial process when I was adding too many traces. Then came Ca / Mg, and ratios thereof. Then came iterations of adding more traces, specifically iron to combat precieved difficency; while it was obvious damage to the plant. Deficiency symptoms don't cause damage in my experience. Depending on the thing missing, deficiency usually stunts growth (except for nitrogen and potassium deficiency that can cause rotting). Extreme cases of micro deficiency really doesn't happen when you are feeding a tank alot of fish food.
Nothing helped my situation but not dosing traces for almost a month, and then resuming traces when I saw something was definitely missing. The first sign for me was pale green new growth on a few species. Rotala Indica, Blyxia, and Hygro Compact not gaining green coloration on mature leaves. Slight amounts of DTPA iron and Gluc immediately made a difference (0.01 ppm of each, 2x a week).
With this type of damage, you have nothing to loose by eliminating traces from your dosing. The damage caused by a deficiency is much less severe than what is caused by toxic effects. It's not like you will be completely eliminating traces, either. Looking at the back of my fish food reads:
Manganese sulfate monohydrate, zinc sulfate monohydrate, ferrous sulfate monohydrate, cobalt acetate.
If after a week or two you observe some plants doing better, some worse, some are even melting. Don't dispair. Trace deficiency doesn't cause outright melting of an aquatic plant within a week. Plants in general are much better at dealing with low levels of nutrients then they are with toxic amounts. In this situation, stay the course. Keep dosing macro's as usual. Let things recover. Reducing light has helped me stave off some issues, and then slowly returning light to high levels after plants have grown past their toxic extremities and the water column is clean.
Some would insist that having a high CEC substrate such as AS or ECO will hold metals and be toxic even after you remedy the source of the problem. This could be true, but as long as your not adding more traces, a plant has much better capacity to uptake metals from the substrate selectively then they do from mass flow.
Let a ludwigia species grow out of the water if you can. Notice how it will grow normally and fully. It's because of the 380 ppm of co2 in the air, right? Perhaps, but there also isn't any micro's in the air. Obviously make sure your co2 is good. This is important; same with flow. But what I'm seeing here isn't co2 deficiency. It's actual burning of plants from over fertilization. A farmer friend took one look at my AQUATIC plants and said, "You're burning those plants with too many fertilizers."
Getting some giant duckweed as floaters helped me. Let them grow out. I was throwing out pounds of the stuff every week when i was detoxing my tank. At first even the duckweed was experiencing toxic signs. After repeated water changes, the duckweed started to grow faster and without symptoms.