Fertilizer and lots of it. I found doubling the pond tabs I was using made a huge difference in the number of blooms. I think in FLorida where the water gets so hot the plants need more food to stay in good shape. I am not sure if it was the temperature of the water or the fact that we had to constantly top off the container due to evaporation and that diluted the fertilizer??? I had my lotus in a pot that was maybe 15 - 20 gallons and I used two pond tabs every other week. We went from just a few flowers to constant flowering last summer.
In December we left FL and moved to the NC mountains. I left the lotus with a friend and just ordered a mini lotus for our deck here. This is true downsizing.

Yep, lots of nutrients and sunshine make for lots of blooms. Warm water makes for good plant growth, which helps, too. I plant in pretty rich media to begin with, below a top sandy layer, but you can't beat pond tabbs in the second year or when the blooms slow down.

Paul, I agree warm water is good but in Fl the water temp often exceeded 100 degrees. It evaporated so quickly we had to add fresh water almost every day.

Sure, we have constant watering here, too, with very low humidity and high temps. We hit 119F a couple years ago. Many things have to be moved out of the sun to protect them in mid-summer. Lotus will get a bit crispy above 110F, but will be fine as long as they have sufficient water. When possible I want the leaves sunlit and the water and pots fully shaded in the summer.

I've heard from people in cooler parts of the country who've had issues, though, in the beginning of the year when trying to start before the water's warmed up, or with a lack of growth or blooms once it cools down again.

Do your temps cool off at night? A major problem in the SE is the hot nighttime temps for weeks on end, they are hard on a lot of plant material.

I have surrounded lotus tubs with potted plants to shade the tub and it helped a little.

Yes, that's the benefit of low humidity and desert conditions. Hot days, cool nights. Helps tremendously with large bodies of water, but not so much with small containers that can really heat up before the end of the day. I've sometimes sunk even smaller containers in the ground to get the insulating effect.

Thank you for the fertilizer advice. I fertilize, but not as much as you each suggested. I will increase the fertilizer to see if that promotes blooms! Thank you each so much for the advice!