Red Mangrove drops propagules prematurely

[Accident]

https://imgur.com/a/Gny2TI have a large Red Mangrove outside in a horse trough and some smaller ones in the same trough. The oldest is at least 10 years old and it's been flowering for around 7 years. The other, smaller tree has been flowering for 2 or 3 years. They do produce propagules that get to about 3/4" and then fall off. Very aggravating. My AC unit drips into the trough to insure it never goes dry. I have researched numerous times and nothing works. I'm in Deep South Texas. Any help appreciated.
https://imgur.com/a/Gny2T

 

[SaltySully]

The trees may be rootbound, I have had tropical fruit trees in pots drop fruit preme when they are root bound. Red mangroves have massive root systems.

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[saltwater sam]

Wow, that's a giant tree you have there! Do you have any special plans for it, like putting it in a tank or a pond? How are your nutrient levels in the water? If the tree is nutrient limited, perhaps phosphorous, it may not be able to produce viable offspring. Is this just one tree or is it two? If it is an isolated tree, the flowers might not be getting pollinated, and therefore are producing nonviable propagules.