I only have a couple of inches of water over my lotus. It does just fine. I've had people express surprise because they thought the lotus should be treated like a water lily, with a couple of feet over the tubers, but I've never grown mine that way. They will do fine in a few inches of water. Also, frogs won't hurt them, and in fact the tadpoles will help clean the water of algae. I'm thinking your lotus may need phosphorous. They're getting plenty of nitrogen from the cow manure, but they also need phosphorus to grow strong and healthy and especially to bloom. Use plant tabs or plant food spikes. Make sure the phosphorus is the highest number.

2 things I can think of.....too much sun? Did the water get too hot? Don't forget to fertilize every 3 mo during growing season. BTW, I need to fill a natural pond with water lilies and lotus for the park. I would love to trade for bulbs or seeds. If anyone can help me with that, please contact me. Thank you!

Here is a link that might be useful: FB

I have a few different kinds of lotus. bowl and normal sized. Some are in plain garden soil others were in a manure compost type mixture, they both only have a couple of inches over the water and stay in full sun. They do get mucked up with algae But the plants themselves do well. This is the second year for the ones I started from seed and the first year for the tuber I just bought at the beginning of the year so here's crossed fingers for their first blooms! I want to know how you got blooms your 1st year from seeds!! Great job!