New Betta fish doesn't move!!
Hello everyone. Came up with an another issue I'm facing these days. I got a new Betta fish yesterday (Thai rosetail) from my local fish shop. When I bought him, he was in a very very little tank, I guess it's like 0.5 liter or something like that. Even at that time he was not moving (Actually not enough space to swim). After I brought him my home and moved into a 20 liter tank (same tank my previous Betta lived happily until his very tragic accident ) he doesn't moving much, Sometime he doesn't move at all. Because of this issue, I can't even feed him. My tank setup is pretty basic with black sand and three live plants plus a sponge filter. Speaking of this filter I replaced it today thinking the old filter is not working properly. But the same issue continuing. Yesterday he ate but today he doesn't eat anything. As the shop staff said he is below 6 months old. As I'm having other 3 tanks, I genuinely think there's nothing wrong with water or temperature. Any advice/idea/experience is much appreciated.
EDIT : I just checked his tank and noticed he constantly open and close his mouth as he chewing a gum.