Just To Say Hi

Hi @Johno2009  and welcome to the forum. 

We tend to routinely use the dH German, and yours being 11.64 is very good as it is within the rage of a lot of fish, with the exception of those that like very soft water.
My water is quite hard (around 16), and I tend t0 use RO water to take some of my tanks down to around 12.

Did you check the nitrate levels on the water company site too? The lower the better, and it's always good to know what is in your tap water.

 

Hi and welcome, @Johno2009

11.64 dH German equates to 207.75 CaCO3 or ppm. The most up-to-date species profiles on Seriously Fish tend to cite fishes' requirements including water hardness/softness on either of these scales. Your situation (water hardness, and tank's dimensions - almost) would suit a betta fish. Alternatively, the tank dimensions might suit a shoal of a diminutive/nano species - the water might be a little hard for a shoal of ember tetras or bororas brigittae, and a little soft for endler livebearers, but we might be able to collectively come up with some additional suggestions for you which would suit both.