Aqua One Aquis 1250 issue

[Mrozu22]

Hi all. It's looks like my filter is catching air a little bit. I marked the water level inside the canister. Somehow it's still running and do the job, but I can't figure out where is the leak.
The main seal (o-ring) is new.

 

[charliebankston]

Sometimes I apply a little Vaseline to the o ring as a water proof seal

 

[Mrozu22]

Sometimes I apply a little Vaseline to the o ring as a water proof seal

I always do this ����