Ive read that whisker shrimp dont get along with RCS very well. Not sure how true it is as I have never had whiskers before but may be part of the problem. If not that then I would guess betta taking advantage of situations and or the soil. Hard to tell.
I know in my 40B community with a decent RCS colony I will lose a few RCS here and there, usually failed molts. Then I will go weeks without any dropping then lose 2 or 3 again. The fish I have in that tank could care less about the shrimp once they are about 3/16 to 1/4" in size.
I'm beginning to get the same idea. Whenever I've seen RCSs in a tank, they were bottom feeders but mine kept hiding either in a top corner of the tank resting on the tallest rotalas or hanging from duckweed. I don't think I've ever seen them eat. My current thoughts are that I either should have let the amanos and cherries get a little more established in the tank prior to adding fish, especially the bettas and tetras. There just isn't enough room in my 4gal for the non-established and non-aggressive shrimp to be with aggressive shrimp and fish. Rookie mistake.
So I'm preparing to set up a 6gal tank that I'm setting up with the same Walstad method that the 4gal is, and will move all the fish and whisker shrimp to that tank as the whiskers really have no issues with the fish.
The current 4gal, I want to keep it just shrimp and snails. I really really want to try to breed cherry shrimp in that tank.
And thanks for the insight with your RCSs. It'll calm my rookie aquarist heart if I see any die for no reason in the future.
I was looking back at past posts and maybe I read it wrong, but thought it was mentioned that you had some die off.
I initially brought home 4 whisker shrimp. One got cloudy and looked like one or two of its legs were clubbing. Like, it almost looked like something was stuck to its foot but as I watched it swim around upside-down and clearly not looking good, it looked more like there was something wrong with its leg. That whisker shrimp died at the end of the first 24 hours. The other whiskers have been molting, and voraciously eating for the last 3 weeks and don't seem bothered at all by the tetras and betta.