Aquariums: Thriving aquascape, 100+ dead shrimp

I built an aquascape in November last year and the tank is looking pretty good. The fish are healthy and the plants are thriving.

The shrimp however, they keep dying. I've probably lost close to 100 shrimp over the past month and a half.

The fish:

– 20 ember tetras

– 40 neon tetras

The plants:

– monte carlo

– dwarf hairgrass

– lilaeopsis

– red lugwiga

– fisseden moss

The foundations:

– rocks

– aqua soil

– gravel

– sand

Everything has been bought from reputable stores, not chain stores, quality aquariums.

We have tested:

– PH

– KH

– GH

– Copper

– Ammonia/Nitrates etc.

– Co2 levels

I also recently used a polyfilter for 2 weeks and based on the colour change it was organic waste.

So i thought id try again and bought 20 cherry shrimp last Friday.

I placed 10 in a breeding box (within the tank) and another 10 into the tank itself. This way I could start to rule out if it was a water issue or something else.

Its currently Tuesday night and 6 remain in the breeding box (4 died3 in the first 24/48hrs). As for the tank, I spotted 2 today and have found 2 dead. I couldnt for the life of me find the other 6.

Id say 70% of the shrimp that have gone missing have never been located. I do see that the bodies tend to decompose quite quickly so theres every chance the tetras pick at their carcuses.

So what in the world is killing these shrimp? How do I isolate the problem without destroying my tank?

I really want the shrimp to work, I see them playing a pivotal role in the little ecosystem I have created. Please! I will be forever grateful to anyone who can help me identify this issue.