That all sounds great. If you are worried about water changes, there probably is no need, in a tank of that size with so few shrimps, and being newly set up, it will be fine to just leave the water changes for a while anyway!
Hopefully you will soon have shrimplets to watch in the tank in lockdown!
That was a popetpop aquarium air bio filter.
It goes by many names. If you search for "aquarium air bio filter" you will find it.
However, these are not very efficient compared to the double filters like these ...
Well guys, thanks for your help. Just a small update. It seems that dosing the tank with oxytetracycline worked like a charm. Haven't had a single death since then, and all shrimps have grown so much! At one point I had 5 berried shrimps! Some have given birth, one molted and lost shrimps, but all good! Look at them feasting and munching!