P isnt really toxic, the problem sometimes is it interfering with something else. That something else is usually Fe, which affects new growth. This isnt that.
Alternatively, too much Fe can interfere with P as well. It "might" be that but it's impossible to say just looking at a few pics.
In the very bottom pic of the first post, is that a stump? I dont see the rest of the plant. The existing leaves from stumps shouldnt be worried about. Especially a very short stump with only two sets of leaves remaining. Those leaves often degrade as the plant reabsorbs mobile nutrients to fuel new growth.
Mature leaves of this plant naturally have a curl around the edges.
Granted some of yours are cupped pretty bad, but a lot of the newer growth looks fine. I dont think the plant is entirely happy but its probably not worth focusing on.
You've made a lot of pretty significant changes lately. We could speculate all day long why a few leaves look that way but I believe it'd be rather pointless.
As Gregg pointed out the grass has a little algae and the red ludwigia looks a little puckered up. So things arent entirely right.
For now I'd focus on good cleaning and maintenance, and keeping a stable
KH, GH and CO2. Need to stop screwing around with the former. Pick something and stay there for a few weeks.