My 2 discus

Here is 2 photos of my discus. They look fat and happy but just would like to know from the guys that know more about Discus fish if they are healthy and all good?

 

How do distinguish between male and female? The second foto discuss has abit of a bell to it?

 

Just the mind the sctrach or two on the glass the tank is almost 20 years old

 

The strong bars are usually a sign of stress. Are they like that the whole time?

 

The bigger discus had very little bars for a time but otherwise they've been like this since i bought them. I just did a water change before the pics so that also should have an influence on the bars.

When i bought them they had the white film over there eyes but got rid off it after a while. Now to think about it once i started to add CO2 on the solenoid to the tank the bars became more prominent. But they not gasping for air and my indicator show ideal CO2 level.
Can it be the diffuser that i use. It make bubbles in the first compartment then bubble's offer to the next compartment and then when that is filled up it makes a big bubble to the top every +/- 20 seconds. That makes a noise as the bubble escapes from the tank. Can that upset them since they hear much better in the tank then we do.