I rarely do water changes (I didn't even note down the last time I did one), and if I do top-offs I make sure the water parameters are an exact match (to the best of my ability). Then I drip the new water in instead over the course of a day. Basically, I try to make sure everything is as stable as it can be.
Oh man have I ever dropped the ball in this thread. You HAVE to do somewhat partial regular water changes with shrimp colonies; that's not optional. I missed this on the first reading by paying too much attention to the parameters and I apologize for missing this key detail. I'm over a decade into keeping Neos at this point and cringe at the thought of all the times and places I might have erroneously said otherwise. I absolutely believed it at the time, but I have lost enough whole colonies finally to know better*. For long-term success you do small frequent partial water changes for dwarf shrimp. Full stop.
Where the husbandry evidence fools the shrimp keeper is when you neglect a tank and they seem to just do better!
"Well, things are stable and they must do best just being left alone! Besides, I'd suck up babies if I were to gravel vac.," we've all thought. But they are reacting to not only water stability but what you had
been doing. When newly acquired imports die in your perfect water, they are reacting to what they have
recently been through. Even though they might hang on for a month before croaking, they were doomed from their shipment from Singapore (let alone the one from the domestic seller). They ARE hardy and adaptable creatures and I've kept Neocaridina in everything from substrate hardened alkaline water to 0 dKH aqua soil tanks using RO. Either way I believe that they need water replaced regularly. I certainly do not know it all about shrimp (or any subject), and don't claim to. I don't test as often as I should -and more importantly often don't record it when I do even though I have a spreadsheet just for each tank's water parameters on my desktop. I can't get a colony or orange eyed blue tigers to take off for the life of me. So take my advice for the experience -and lack of -that I freely admit. If your source water is consistent, change a little of your water every week. If this was my own tank, I'd do 10% every other day for a couple of weeks, and then see where they are after that. Using your gravel vac. I'd be cleaning filer pads and rinsing sponges where applicable. Anything in your control to make a cleaner environment. And if you change water regularly with the same source water, you never stray too far from that, and that is what the shrimp adapt to.
*For a good 5 years I had unheated planted tanks (with no fish) in my garage addition fish rack that reached high 40's in the winter. I sporadically fed, kept whatever leftover reef lights I had on a timer, topped off with tap all the time, occasionally water changed and maintained, and most did acceptably and there were hundreds upon hundreds of shrimp in some of them. But time caught up with me in each one. When I had losses -and they were inevitable -I typically lost the whole tank full. I've yet to completely figure out shrimp, but I am positive that over the long haul, small partial water changes are crucial.