They're doing well, establishing their territory. I added a coconut cave for them today, and tonight they are doing the 'mating dance' even more actively. The female surprises me, it chases away my biggest female betta (i have 3 in there with them), which is almost twice her size. I also added some peat to my newly aquired filter (got two fliters running on that 20 gal now), so the lowering of pH might have something to do with the courting behaviour.
Once they do spawn I plan on setting up a seperate 10 gal for the 3 female bettas, have an extra seeded filter, so they can be moved pretty quickly.
The pic doesn't really do the male justice in his colouring, but I have to use flash because he wont sit still long enough.
Tnx for the comments!