Why aren't my dwarf puffer breeding?

[pjeterschornstein]

Hey!
I have 3 dwarf puffer. at the beginning when they where smallI put them together but I figured it's two males and one female (it's still hard for me to tell. one have a line on his stomach and the other one I think as well but less defined) they aren't breeding though. I have extremely hard water here so I use a reverse osmosis and put half together with tap. temp is 25c. It's a 45 liter low tech tank very heavily planted. parameters are always good, PH between 7-7.6 , there's never any NO2 or NO3, GH is >7, KH 6-10.
I feed them grindel worms, scuds, dephnia, little pond and ramshorn snails.
There are some clown killifish with them now who are also not breeding for some reason (I have them for two years maybe...)
The other one stayed in a different tank with dwarf bumblebee gobys for now.
anyway, what am I doing wrong here? the little guy is keep chasing the female but she just escapes in panic ( same as the killifish...)

[Pufferpunk]

https://www.pufferfishenthusiastsworldw ... vancoricus