Everything seems to be thriving, the level is very consistent, so I’m not going to attempt to mess with anything.
My one female is still berried, we’re at about the three week mark since I first saw the eggs. Lots of moss for them to hide under.
Your Caridina should be fine with that PH, it may be the new substrate and setup causing it to be a bit lower than you expect but if my previous attempt is anything to go by it should creep up very slowly as the tank settles and matures! My prior tank setup started at PH5.5 and all was well, and the current setup is PH5 though the next colour change is PH6 so it could be anywhere between those figures???
Hope the berried female is still doing well, or has she had her babies yet? Babies will be microscopic and hide to start with.
The photo is not a DAS. The only place I know that breeds DAS commercially is Aquagreen for half that price. https://www.aquagreen.com.au/catalog.html
I do keep them and have bred them in the past but I don't have any excess at the moment. I'm going to try and breed them again this summer. They have marine larvae so are not easy but on the flip-side they live for 5 years or more and are hardy.
The photo at that site looks to be a Paratya which will also eat filamentous algae but not as voraciously as DAS. My Paratya came in the mail from https://www.livefish.com.au/tropicals/shrimp-and-crays.html
You can get them in local rivers but I find the ones from livefish do better in warmer tanks (Livefish are in QLD) - these breed in fresh water in your tank (easily).