I have kept both of those species and I live in Somerset, I know it doesn't fix your present problem it may be worthwhile to acclimatise them to your tap as it will save a lot of effort in the future.
Makes water changes easier anyway
Thank you, Simon that helps a lot. I'm wondering if I was too quick to jump on hardness as the reason my first fish died - I think that being a newbie, I wasn't as discerning about who I took advice from as I am now and didn't have the knowledge or confidence to diagnose exactly what was going on. 🙂