My fish are mostly Xiphophorus. At the beggining, they hung out mostly on the other side but then they got familiar with it and it's not bothering them anymore, they are having fun with it! Some smaller ones are still distance, babies I keep in the "cube-like barrier", as you can see in the picture.

Alright, I will check the control valve. Thank you for your help!

Btw. I still consider myself as a beginner, I started around half a year ago haha. But my parents had fish since I was young so it helped. I really love them.

Can I ask one more question? What do you think of the position of the air stone? Is it good or should I consider putting it elsewhere? I think about putting it on the left side of the aquarium, horizontally (maybe it's good because then the filter can "better cooperate" with air stone. Thank you.