GodFan, i haven't looked into the scarlet Badis specifically, but hessitate one one principle alone
diet, ...
when i was initially looking for the apex preditor (if that's the correct way to refer to it), the big guy at the top of the food chain ...
i searched, and ask for assistance in my search for omnivores with a preference towards plants.
before i was suggested the florida flagfish results were dissapointing.
-herbivores typically start at 6"+
-omnivmores typically start at 4"+
unless i'm looking into huge tanks for an experiment those are insanely huge fish for a hobbiest for such an experiment
the florida flagfish at just over 2" was perfect for me
well if i had the choice of smaller i would, but i haven't seen anything under 4" that cared about plants of any sort (including algae)
plants grow, they consume nutrients, but plants are needed for self-sustaining so the fish don't kill themselves with nitrates in the water
i wanted a system where the plants would be kept under control by the fish, but still have plants
the flagfish is very small, and despite it's dietery preferences i've found a problem, ... the reason most herbivores start so large is their mouth is big enough to do damage to plants, ... so the flagfish posed an aditional problem, finding plants with leaves small enough/fine enough the flagfish can nibble on, ... searches for that ... well i've got a physical description as asking around hasn't given me much for answers
the scarlet badis you suggested, ... would let algae and plants run out of control till leaves accumulated that would be blocked out from light or run into deficiency problems that would impair the health of the plants and i worry about that unsettling the balanace in a self-sustaining aquarium.
one day i may consider larger fish (other omnivores) or even herbivores (which would allow me to use bladderworts that would allow zooplankton that could eat phytoplankton, that would assist with ensuring nutrient levels in the water column don't get excessive. ... but that's a possibility i'll consider another day.
for now i'm using flagfish for what it helps and the problems it adds
meaning i am also doing what i can to ensure plenty of algae growth, ... which if the nutrient levels being released by the substrate are sufficient to allow for high density greenwater that i require help at keeping phytoplankton levels down, ...then there will be suffient nutrients to allow algae in the tank that i know the flagfish will eat
... it's all based on ensuring the diet of the apex predator (if that's the right term in this situation)
others i've seen consider & talk about their experiments with self-sustaining tanks, ... treat it like guppy/endler fry don't need food (but they need some form of bacteria or phytoplankton (or even bacterioplankton) in the water they can eat till they are large enough to eat zooplankton, ... to be sustainable food for the betta (as one example i have heard)
also heard of a lady who heard betta fish are a great way to keep guppy populations in control, ... she finished off her story with the guppy population ran out of control, and she had a fat lazy betta, ... didn't work