When I got my tubers from Texas Waterlilies, they included a culture sheet that said lotus are heavy feeders and need full sunlight, Becky.
Yours look really healthy, but I think I would try giving them a good dose of fertilizer. Do you have the fertilizer tabs made for water plants? About 6 tabs for a large lotus plant each month. If you don't have tabs, they recommended using a time-release fert, about a tsp. tied up in squares of newspaper. Six or 8 of those little 1tsp. packets per plant.
I'm pretty sure mine had limited blooms because I only have about 3 hours of good sunlight hitting my pond. Not a thing I can do about it either, because it is the house that shades the pond.
