For nutrients you could put some fertilizer tablets in the pot. Put them toward the side of the pot so the roots have to grow toward them. There are pond tablets, or you can use aquarium tablets, or even Osmocote in a gel-cap, just like for aquarium use.
Odd that the leaves gave up, but good that you see more. Did some change happen, such as temperature, or suddenly more sun?
I need to.
I need to make a trip to the local nursery, get some fertilizer tabs, and some marginals and floaters...
Its strange.. It threw out some leaves.. And all off a sudden threw out tony of giant sized leaves. So many that it covered the entire pond. With all the leaves overlapping and in piles.
They rotted away.
All at once.
And now its about to throw out a new batch of smaller leaves.. Learning its environment maybe?