U tube air bubble

[jpontier212]

I have a glass 55 gallon aquarium with a Hob overflow box. I have been running a limewood block bubbler in the sump but I'm getting a big air bubble in my u tube which is making a slower flow in my aquarium and I'm concerned that it will one day stop the siphon. I only run the nano bubble treatment from 8:30 pm until 4:30 am when i get up. What can i do to prevent it from stopping the siphon? I was told the only stupid question is the one you don't ask and as you know, I'm a true newbie

 

[Waters]

It sounds like you might not have enough flow going through your u tube. As long as both ends are submerged and you have the proper flow, you won't see any air in the tube. Can you increase speed of the return pump feeding your tank?