I teach A-level Chem (among other things)Goldfish said:*tries to remember GCSE chemistry*![]()
Endler's should be fine in London tap water. Boiling would soften your water, provided you filtered out the limescale produced. I guess the cats would prefer that, particularly for breeding - but I'm no expert about them. A little box filter of peat, and some carbon in another filter would help - and I don't suppose the Endler's would mind too much.
Rainbows are nice and more active than most killies - so they are an interesting alternative. I'm sure you know the brilliant website (very high quality photos) Home of the Rainbow Fish
Alan