Good that you moved the skimmer, we'll see in a week or so if the new leaves keep developing creases.
People often blame nutrients for strange plant symptoms. I've often had people swear that their plants have potassium deficiency when in fact it was their pleco eating holes in the leaves.
These are the nutrients plants need:
- Immobile nutrients are: Ca, Fe, B, and Mn (signs show up in new growth)
- Mobile nutrients are: N, P, K, and Mg. (signs show up in old growth 1st)
- Variably mobile nutrients: Cu, Zn, S, and Mo. (signs show up mostly in old, but can also show up in new growth, or both).
Looking at the position of your damage - in the middle of the plant - you'd have to agree that this isn't exactly new or the oldest growth. So we can rule out all immobile elements (Ca, Fe, B, and Mn) since new growth would show up with troubles and new growth isn't affected in your tank. That leaves mobile nutrients and variably mobile nutrients.
Mobile nutrients are all out of the question because the symptoms of those are very well known and your plants completely don't match at all. That leaves us with variably mobile nutrients Cu, Zn, S, Mo which the symptoms don't match either. All of these variably mobile nutrients show dead spots or patches of leaves in various locations, not lines. In addition, these nutrients are needed in such tiny quantities that it seems extremely unlikely that anyone would ever see a deficiency of any of these nutrients. Using aquasoil in your tank makes it especially unlikely that you have a micro deficiency since aquasoil has all the micros in it already.
This leaves us with the final conclusion that it is not and cannot be a nutrient deficiency.
From the link you posted above:
Originally Posted by zenkatydid
i have indeed experienced this, and it went away when i increased trace dosing. i don't know what caused it, but it was something in there
Just because other people recommended adding micros doesn't mean it will work. Better to look into the existing research and see what symptoms match your problem eliminate everything you can like we did above, then look for other reasons that could cause the problems you have (mechanical damage).
Anyway, do post an update in a week or so and let us know if moving the skimmer helped. I would try change only one thing at once, so don't follow other people's advice until you have eliminated the possibility that it was the skimmer damaging the plants. If you try many different solutions at once, you'll never know what actually fixed the problem.