Thats a bummer. Were the other tanks shrimps also or is there something else that is maybe hardier in those tanks?
As far as your pond I would be more suspect of the bullfrog. Those things will eat anything and are pretty darn quick under water. Maybe its time for a rehoming. Oh and they are night time hunters as well when your fish are trying to get a nap in. Makes sense they would be more vulnerable at night to a predator like that.
What kind of newts are that small? Out west here the newts and salamanders are all decent sized.
There are shrimp in all of my tanks, but much hardier Neocaridina.
Yeah, I am beginning to suspect the bullfrog needs to be netted out and driven to the local stream. If he's the culprit, he's sure done a quick job! But no reason to have a predator by the pond with such small fish.
As for the newts, they're the easterns that are bright orange when on land and brownish as aquatic adults. Wasn't accurate to call them withe cloud sized, certainly weigh more than 3 white clouds, but small mouthed slow swimmers. I would be sad to have to remove those.
I don't suppose your lawn had any pesticides on it?
No, I grow vegetables and have the pond so never use weed killers or pesticides. The closest neighbor is 50 yards away, but I suppose it possible something came from her property.
How old is the tank?
Right on 4.5 months according to my set up post.
As of this morning, the survivors are still alive. Still not swimming through the water column or being active as they used to be. At least one lightly berried female remains so maybe there's hope. I think I'll let the tank run for several weeks before considering adding more. Also, I tested the tank with a few cherries after setting it up and missed two when I went to remove them. Of course they are doing just fine. Whatever I did was toxic enough to wipe out CRS but not cherries.