We have three hardy lillies in our pond which is new this year and
doing great.

One of the lillies has gone sickly. It put out a flower and then the
pads begin showing up full of small holes circled by a black band. It
started to put up another flower but that stopped and finally flopped
over before reaching the surface. The new pads are doing the same
thing.

I feed all of the lillies half of a fertilizer tab every three weeks
or so.

Any idea what the problem might be?