A major problem for me has been getting seedlings of various brachyceras hybrids to begin to make floating leaves.
Some seedlings will remain in their underwater rosette stage for many months. I discovered that these stubborn seedlings can be forced into making floating leaves by treating the seedlings with gibberellic acid.
In the past, I have used a 1:1000 solution, but my current solution of 1:1500 works just as well. I remove the seed tray from water, pour off the water, and apply GA with a medicine dropper, one drop on each seedling.
Then I cover the tray with a plastic bag overnight. The next day, I return the tray to water. Within two weeks, many seedlings will begin to make floating leaves, after which they continue to grow in size, and eventually become blooming plants. Interestingly, the Aussie hybrids and ISG Aussies never seem to need this GA treatment. They make floating leaves within a month or two of germinating, if light and warm temperatures are suitable.