Oily film on water surface.

[jaypeecee]

I don't think why the airstone works is known, but the effectiveness doesn't seem in dispute. One theory I've read is that when the bubbles break they fling the biofilm in every which direction, some of which winds up getting flung outside of the tank.

Hi @Andy Pierce

Many thanks for your reply. I was beginning to think on similar lines to what you have said above. But I wasn't sure if my imagination was just having a field day!

JPC

 

[NatalieHurrell]

To the point about skimmers and shrimp safety, I have seen shrimp get swirled around in the airstone bubbles without apparent ill effect. I wouldn't say they enjoy it since they don't seem to actively seek out free bubble rides. This is different from the way the shrimp do seem to seek out sitting in a water flow over a surface: River run - Fireplace aquarium (see the 'shrimp on a shelf' video). Weird but they do this all the time. I think there is some kind of "swim upstream" instinct in these guys.

I've observed it too. Ours are the first in the queue at waterchanges for bubble rides and have a mad half hour every night, doing laps of the entire tank going against the flow!

 

[fredi]

I don't think why the airstone works is known, but the effectiveness doesn't seem in dispute. One theory I've read is that when the bubbles break they fling the biofilm in every which direction, some of which winds up getting flung outside of the tank. I suspect that by keeping the surface film mechanically disrupted the biofilm material either settles out onto the surface or is trapped in the filter (if you have one). in my non-filtered shrimp-only tank the airstone keeps the surface clear and I do seem to notice some amount of "flingage" around the bubbles but couldn't say whether that's how a meaningful amount of surface film is disposed of.

To the point about skimmers and shrimp safety, I have seen shrimp get swirled around in the airstone bubbles without apparent ill effect. I wouldn't say they enjoy it since they don't seem to actively seek out free bubble rides. This is different from the way the shrimp do seem to seek out sitting in a water flow over a surface: River run - Fireplace aquarium (see the 'shrimp on a shelf' video). Weird but they do this all the time. I think there is some kind of "swim upstream" instinct in these guys.

Is it possible the the bubbles break the surface tension

 

[Andy Pierce]

Updating on the airstone, when mounted on the upper side of this open-topped tank the stone did fling out a significant amount of water and debris, so much so that it was becoming problematic. I moved the airstone to the middle bottom of the tank and that has fixed the flung-debris issue and the biofilm has not come back either (video link: Airstones can be messy - Fireplace aquarium). I'll keep track going forward but it looks like an airstone prevents biofilm formation by mechanical surface disruption. I don't know where the biofilm-disrupted material goes... hopefully into the water column and onto submerged surfaces so it can be eaten by the shrimp!