I havee been through your betta post, I must have been through it before as there was a post by me, but it was years ago. It was very interesting and a shame most of the photos have now gone.
Probably a similar time ass your thread I went to my local garden centre and they were doing away with the pet department (assume it was losing money) and clearing that out. I saw a 20L bare tank that had 3 betta which looked like females that they were going to discard as they were 'left over' so I said I would take the fish and the tank, and they agreed. I didn't really want another tank but decided I would put it next to the kitchen sink so I ccould watch the fish whilst I did the washing up. The 3 betta never appeared to get on but I only ever saw them when in the kitchen. After a week or so suddenly I saw a lot of what I first thought were baby daphnia, but turned out to be around 100 baby betta, one of the 3 adults must have been a male (short fin so looked like a female) and that would have explained the agression? Now what do I do, I had no idea what was involved in raising babies and anyway was involved in a large project at the house at that time. Ordering anything online would take days to arrive and set up and I didn't have the time to drive around and pick bits up from various places. I did order some micro worms as food from ebay, you feed the worms yeast, and they arrived a few days later. The baby numbers dropped each day (all in that tiny 20L tank still) but I did manage to give away the 3 adults and about 10 babies before shutting down that setup. So I have a bit of experience of what you went through, and why you wouldn't want to do it again.
I did have the frogbit for sometime, then tried the larger water lettuce, but they both grew (espcially roots could grow a foot in a week) way too quickly and then I got the duckweed, no idea how that got in there, that stuff is virtually impossible to get rid of, without starting afresh. When I moved I finally irradicated it as the tanks were closed down for moving.
The betta I have now is just white with long fins and tail (not dumbo), I told freinds not to get a white one for me, but it actually works so well with the dark tank and black background, so I can see him from across the room! I do suspect he eats the young shrimp though, he is often watching something on the bottom of the tank! I rarely see more than a couple of shrimp at a time and we haven't had any heat above late 20s here this year to have killed any?