They may slow down/stop breeding in winter remember but that's not something you need to worry about at the moment.
I think most people leave at least the back (I leave back and both sides) alone, to grow algae/biofilm, the babies especially like that? If you don't like seeing the growth on the back glass then you can get some black background to put behind the tank, this will also show the shrimps off better, especially babies if they are on the back???? Also as the sponge is black and the filter is also black etc they won't be so visually obvious????
Always great to hear a success story so thanks for the update!
GO FOR IT!
As I wrote earlier mine are kept in KH2 and KH3 and do fine so I would think yours will be as well but just stretch out the acclimating as a precaution. My KH3 I use KH elixir which I got from ProShrimp but that was for the betta - incidentally using the elixir also increases the TDS, but I would go get those shrimps and see how you go first before trying to complicate things as I think they should be fine, so see how they go and expect maybe 1 or 2 may die in the first couple of weeks (expect that and if they don't you will be happier).
As you say the soil is probably softening the water and that will stop eventually, so over time it will probably increase slowly, but my shrimp have lived for 5 years in KH2!
Do you know what the TDS figure is now?
A small update. I have more shrimplets than I can count and numerous berried females too, which is great. I can see shrimplets of all sizes too, which indicates they're surviving nicely. Super stoked to see the population finally taking off.
I imagine switching to RO water has been partly, if not totally, responsible for the uprated breeding and shrimplet survival. The pH has slowly dropped to around 6.8 since I started using it instead of tapwater. I'd also give some of the credit to the warmer weather with the change of season, but I've been here before and never had more than a couple berried at any time, and never had large numbers of babies.
I realised I hadn't put a tank photo up recently. I cleaned it out months ago to make it easier to see the shrimp. This tank is really ugly, but its practical and the shrimp like it. I even leave the algae build-up on the rear glass in case they get something out of it haha.