Leaves... so neatWater that's newly added is often low on oxygen, since it's been sitting in pipes and water tanks and such for awhile. Most likely that's the issue and your smaller fish are okay because they don't need as much oxygen. I'd suggest adding an airstone of some sort, possibly just after water changes.
Also, angelfish top-hug with their entire forehead pressed to the water's surface sometimes if they're feeling nervous, or if they're just trying to relax somewhere safe. They're pretending to be leaves when they do that. If yours aren't breathing particularly fast, they might just be a bit frightened by all the disturbance.
Thank you. That's a good idea. And now that you bring it to my attention, I always used a garden hose on mist until I moved the tank.I fill my large tanks with a hose, putting my thumb over the hole in the pipe to spray the water in a fan so it can pic up oxygen and gas off chlorine etc.
When I use a bucke, I use the hand shower thingy in the bath to spray the water at the bucket from as high as possible while still catching most of the water, like rain.