El Roberto wrote:

I'm using a 21 litre tank,


I may have missed where you're from, but the 21 liters implies you're not from
the U.S. :-). Here, a 10 gallon (41 liters?) is pretty much the standard
starter tank, and a lot of folks on this group will tell you that's too
small.


a) Any suggestions for a good starter freshwater fish that is pretty durable
and won't grow to a huge size? I want something quite pretty so am prepared
to pay a bit over the usual bog-standard prices....


About the only thing I'd put in a 5 gallon tank is a betta or a half dozen
white clouds or neons. BTW, in spite of common beliefs, a betta will greatly
appreciate a heated tank. But it's hard to get a decent heater for your
small tank. The white clouds would be your best bet - no heater needed if
the tank is in a heated room.

If you want, you could plant a small cryptocoryne. The white clouds would
look great swimming in and out among the leaves.

--
It's turtles, all the way down