Seam imperfections  

Seam imperfections

Hello everyone,

I've encountered a little problem. I'm new to 3D printing and would like to know is it possible to make printed cylinders look better. Every time I print cylinders I get ugly seams with little holes/air pockets. (photo below)

I've already done and tried these steps:

What I have already done before:
1. Calibrated the filament flow. Everything is top notch. (and re-measured filament which is 1.74mm)
2. Calibrated extrusion multiplier.
3. Tried reducing printing speed.
4. Lowered retraction length to 0.6
5. Lowered z lift to 0.4
6. Tried lowering z lift to 0.2 and adding extra length on restart 0.1
7. Turned off retraction on layer change
8. Tried printing temperature tower, stock temp seems good, but tried printing it on 225 celsius.
9. Increased deretraction speed to 50mm/s.
10. Turned off retraction.
11. Changed seam postion to rear, aligned or nearest.

Everything was done changing one setting at a time (except 1, 2 and 6). I've saw no difference at all after trying these different settings. The only thing that was noticeable is seam position, I can put those little holes on top of each other and make unified seam but is it possible to reduce the holes itself? Or am I too picky? What should I try?

Thank you:)

P.S. one more photo