Hey guys I’m kind of new to to tropical scene. So a few days ago in an established tank I changed the substrate from gravel to a black sand. 2 days after that I introduced a pearl gourami and 4 panda corydoras. For the first 2 days my gourami was swimming around a good bit hanging out by the fake plants. She was eating with no problem. At the time my local pet store said that she would be fine in a 10 gallon and now I’m seeing mixed reviews. Yesterday morning I noticed she was laying at the bottom of the tank. Since then, she is still laying at the bottom, not sideways or anything, and occasionally comes up the the surface gulping some air. I did a partial water change and nothing has changed. I don’t want to have her die already because this would be the first fish I have lost in a short amount of time. Could it be because she feels crammed or is it one of those gourami viruses. Any help would be great!