Bettas need neutral water and can tolerate a mid range of heavy metals in the water column.
Also, lets think about this "animal"
Its a fish with more brain interactions than the majority of fish you can find in stores. They will learn your patterns, will recognize you, can be trained and can fight till its death, creates a nest of bubbles above the water and can learn behaviors. Might be that you need to stimulate your betta, if in a 10g without any other fish with not too much interaction they wont survive and depression will kill him. (Im not saying that by being a breeder but by nature and research)
My pet betta is trained and analyzed everyday for 30m-1h so i can stimulate brain activity. I also have plants and small snails as you can see in the pictures. This tank was suppose to be another farm but i added a fish in the cycle for study.
Make sure to:
Test your tap water before addjng conditioner to check whats in it already.
Too much light can be an issue in small tanks like 10g or even 20g. Im using a weak led
Stimulate him before feeding anthem, when u get his attention, you can start doing a specific (delicated) tap with your finger nail followed by food at the surface.
I hope this improve your ecossystem (;