Hey gang I have a mystery that I can't seem to figure out.

In my 20 gal tank I had 3 ghost shrimp that were doing great and I added 25 red cherry shrimp. Since add the RCS I have noticed they are dropping like flies. Like 1 per day at least. And even 2 of my 3 ghost shrimp have died now. I can't figure out why.

I did treat the tank with tetra parasite guard a few weeks back before I added the RCS. I did move the ghost shrimp to a different tank at that time. After I was finished treating the tank I did a huge WC then added the ghost shrimp back. They seemed fine once back in the tank. Once I started noticing the RCS dying everyday I thought maybe there was medicine left in the tank so I added a carbon bag into the filter to remove it, but they are still dying.

I paid almost $50 for my RCS and if I have 10 left alive right now that is a lot.

What am I missing?

Most of the fish in the tank are small so I don't think it is them killing the shrimp. I did add a Pearl Gourami to the tank a few days before I added the RCS. Could the gourami be the killing them?

I would like to restock the tank with shrimp again but not until I can figure out what is killing what is in it now.

Water parameters are good: ammonia 0, nitrite 0, nitrate 10, ph 7.4