Dealing With Hard Water

I am sorry if there are some existing threads on this topic, I am sure it is not new. But I could not find anything sharing the advice of experienced fishkeepers.

I have been cycling with treated tap water, and I think I am close to finished. I understand I need to be a bit cautious with the water readings, I have very high nitrates still. But I am sure I have hard water – 349mg/l CaCO₃ according to South East Water* - and pH of about 8.5. (I only have combi strips for Gh, KH and pH , I have proper test kits for ammonia, nitrate, nitrate. I wouldn't mind buying more proper tests if an exact reading useful. But it seems like an imprecise reading might be enough to tell me where I stand).

My local MA said two things to me – they sell RO water to a lot of people, and they specialise in hard water African Chiclids, but even then, only a few of those are happy in the local tap water. From my point of view, I’m still not 100% decided on fish – but if I finished cycling tomorrow I would like to buy ten Zebra Danio, and maybe add some YoYo or Dwarf Chain loaches, and some TBD Gourami later. So nothing unusual, but still I think my tap water not great.

I was thinking of doing 50/50 tap water and RO (the expense is ok, but I don’t want to be lugging more big containers of the stuff about than I have to!). I’d be grateful if anyone has an opinion on what they’d do if they were me, or even better what they did themselves. Feel free to be blunt if I am showing my ignorance – I have tried to do the reading and be organised, but to date my real tropical fish keeping experience is zero days!


*call me a cynic, but, since they call 350 excessively hard, I am suspicious someone might have worked quite hard to get it down to that on the day they tested. It looks > 20 German degrees on a JBL test strip. Also – I was irrationally annoyed Thames Water’s website could not tell me. I know I pay South East water, but I can see the Thames from here!