Hi Helene.
I understand your doubts – and I share(d) them, too! Therefore, the decision to have 10L tanks (instead of say 25L) was not very easy to me. But as I wanted at least three small tanks in a cupboard-like housing, 75L+ of water seemed too heavy and voluminous.
And up to now, due to very regular water changes and conservative feeding, the 10L setup workx rather perfect even for the bigger Bettas!
The 13+ young B. tussyae are close to 1cm now, so the adults will have to move to my bigger living room tank for a rest soon enough. The 2.2 B. hendra already moved their – and the 3.3 P. nagyi were devided (1.1 and 2.2) onto two 10L tanks after a first couple showed up. And… But no! You will have to read my P. nagyi diary to find out more. 🙂
Michael