Aquariums and Fish Keeping

First of all I want to thank you guys for helping me identify my eel. I haven't felt this kind of help in a small community anywhere else.

Now for the tetra's we had a dissappearing issue when we had a rainbow shark. We ended up getting rid of the shark and getting tetras till we had 20. Now we're down to 12. I currently have 3 swordtails, 2 loaches, a small brisslemouth pleco and a larger pleco that survived. Plus 2 eels, one that was answered here and another is a zigzag eel.

Am I having a problem with hiding spots? I know I don't have enough plants. I'm thinking of getting more moss and covering the area under the wood structure on the right.

Or are they getting sucked up the filter? I thought this but couldn't find any evidence in the filter system. Any advice would be fully appreciated.

Here's the pleco I'm questioning.