One of our local nurseries stocks aquatic plant supplies, and they
sell a fertilizer tablet that's about the size of a nickle and 3/4 of
an inch tall. I don't recall the brand, but they are sold in bulk for
10 cents each. You just shove 2-3 of them down in the pot about once
a month through the growing season. I start fertilizing in May and
give them their last dose in August here in Zone 6. Seems like an
economical and effective way to go for my pond. I always get lots of
lily blooms and the plants look great. Never tried them on tropicals
but they work great on the hardy varieties.
Gary