Welcome fellow UK shrimp keeper!
I agree with shrimpnewb above, those parameters seem way off though cherry shrimp are quite robust. I have cherry shrimps in with a lot of nano fish and it is densely planted.
1) Have you tested the water from the TAP, the water in the tank may be building up GH/KH/TDS if you are topping up with that for evaporation?
2) I haven't ever had a problem exactly the same as my cherries do well with tap water but we have fairly soft water here I think. You may want to read this and go this route (ie RO water remineralised) and if you do you can just start doing it in replacement of what you do now (ie use the new water for water changes, and use pure RO water for topping up) so it will be gradual enough to not upset any livestock, albeit it will be slowly changing so you may still loose some in transition, but that would probably be the way I would do it. I think it covers most things but if you have any questions just let us know. It is so easy with the zerowater jug which I use and would recommend for the small tank you have (www.zerowater.co.uk).
https://skfaquatics.com/forum/forums/topic/14025-tap-water-taiwan-bee-uk-zerowater/
3) When you do water changes you should slowly add the new water, most people use some sort of dripper, I use one of these but some people create their own.
http://www.onlinereptileshop.co.uk/reptile-products/Drippers-and-Sprayers/Zoo-Med-Big-Dripper-Bd-1-3811.html#sthash.8tel5oAX.Txucpw12.dpbs
4) It is easy to over feed shrimps so do that sparingly, ie half what the packages say at most, they are in it for profit remember!
I can't think of anything else off the top of my head, the setup sounds ok and 10-15% water change per week sounds fine, Ph same as mine etc. As I say, just ask if you have any specifics you want to ask.
Simon
Ps if you want anything I use these people.
https://www.pro-shrimp.co.uk/