Anyone here use a liquid fertilizer in there pond?

I have the dry ingredients and make liquid fertilizer for my planted
aquariums. Does anyone use liquid fertilizer for their ponds ? My water
lettuce does not seem to be growing like expected. I also have a few pieces
of duckweed that have not taken off to multiply into
3,000,000,000,000,000,000,000 so I figure something is missing the plants
need. I guess I could pull out the test kits I use for the aquariums and
check it out.