Can you please tell us if your tank has fully cycled, how long has the tank been established? This is very important.
If the tank isn't cycled you will have problems - but if it is, I do feel that you are still overstocked - even if you have excellent filtration as alex mentioned, doesn't mean that fish will always be fine - space is also a big issue & needs to be taken into consideration. Often tanks eg: 170 ltrs - don't necessarily hold that much water because you have to allow for gravel/decor etc. which take up water space, so it will probably hold less than 170 ltrs. Just wondering how often do you do p.w.changes btw?
I feel that you may have problems having the betta with dwarf gouramis & tiger barbs & aggression may be an issue. You mentioned in another post about your male betta, it could also have been caused by the other fish & not just the female bettas.
If you have male/female livebearers you will also get fry & the danios will breed like crazy as well.
so you may end up with a lot more fish!
It does sound like a lovely tank though paddy!