CO2 Diffusion

Is there a linear relation on CO2 diffusion in Hard/soft water ?
I ask this because yesterday on my weekly water change I've added 25% RO
water.
What I did notice is that at this stage (GH was lowered by 2 degrees) that
the CO2 diffuses much better. before the water change, the bubbles were
diffusing to the water but some still made it to the top, but now you can
hardly see them climbing and they are diffusing much quickly. I can really
see the change since there are like dozens of them floating in the water
till they disappear.
So can one assume that CO2 does dissolves better in softer water ? Or this
is because of the changes in KH ?
10X

Gizmo