The plants on rock are some mosses, peacock moss and java moss.
I am suspecting three factors causing the death, more than 15 died.
Suspect 1 : The top part of the wood is exposed to the air and it is still wet, there are some white thing growing on it. When I was rescaping the tank this white thing went into the water. This might polute the water and kill the fishes.
Suspect 2: The angel fish is being very aggressive, I saw her killed some red cherry shrimps and hurt 2 puffers.
Suspect 3: Poor water quality as I hardly got time to change water recently.
Suspect 4: I bought some freezed "red worm" for them and it might be contaminated.
I have listed feel factors which might be the cause of the death. I have eliminated the second factor as most of the bodies did not show nipped scar or I should say the fish still look good when they died.
I also want to kick out the forth factor as I use the worm for other tank too and the fishes in other tanks are alright.
I have done WC recently... Still observing...
Will post pics too...