Thanks for that, I think I will try that just so that I know, though I don't think they will be going back into the tank now.
Will be good to know though whether they were the reason.
edit 1hr later - I have done this, and also put some of the water in a cup to test the water itself, will leave both a week and report back. Ph was 5.5 when set up
My guess is a fungus, so remove it as much as possible and do water change (slowly).
The common causes of fungus are overfeeding (left over food), something that is decaying (plants or animals), or something emitting sugars, like driftwood.
All the other parameters are stable and perfect, and the newly filtered remineralised water that goes into the tank when doing a water change is Ph5.5.
I use the dennerle mineral double in place of salty shrimp as it is easier to use being a liquid!
I do 10% water changes each week.
It is a bit baffling to me but as there is no obvious problems at this point I am not too worried but will probably get some new substrate ready, just in case. The substrate that is in the tank is a year old and as mentioned the only other unknown that may have caused the problem was I had 3 geodes in the tank, which are a type of rock?
I leave the sides and back alone as well and the shrimplets seem to come out onto that a lot and IF there are new borns that is the only place where I get to see them.
When you do a water change you need to add in the new water very slowly also, most use some sort of dripper setup.
It may just be that the setup wasn't established enough, that is what I put my fungus down too anyway. Mine wasn't really anywhere that I could remove it but it cleared in less than a week, but if you can remove some manually I would do that.I imagine just adding the shrimp may cause a small/temporary imbalance as it then has to adjust again, if that makes sense?
Hopefully you won't loose any more shrimps, and I wouldn't worry too much about the fungus unless it just keeps getting worse, as I have had this happen a few times with newish tanks and it has always just cleared up in about a week.