Big bubbles during diffusion

[octopus]

I hope most of you agree that for effective difffusion, the bubbles from the diffuser should meet some resistance to be effectively dissolved. Initially when diffuser bubbles were allowed to rise without any resistance i could only notice tiny bubbles. But after repositioning it to come into contact water discharged from the rain bar, there appear to have big bubbles among the tiny ones rising to the surface. Can someone enlighten me on this. Hope there is no cause for concern.