The airstone does a great job of keeping the surface of Shrimphaus clear from biofilm, but how it does that exactly isn’t clear. One idea is that when the bubbles break on the surface they fling water and biofilm in random directions, including over the side of the open topped tank. For sure this flinging of water happens, whether or not biofilm goes with it. This leads to a gradual build-up of minerals on the sides of the tank above the airstone from broken bubbles after the water has evaporated. I was going to be ok with that, but it turns out the amount of water flung over the side is sufficiently substantial as to wet the wooden surface of the table supporting the Shrimphaus. Wet wood is not a good idea so this is a problem.
Try putting the airstone in the middle
I’ve moved the airstone to the middle of the tank on the bottom. In this location the bubbles spread out evenly over the surface of the water but don’t get close enough to the sides to fling out water (and biofilm), or at any rate this happens to a greatly reduced extent vs with the airstone mounted on the side wall of the tank. This arrangement of having the airstone away from the walls will be a pretty good test of whether the main mechanism by which an airstone removes biofilm is through simple mechanical disruption in which case the biofilm won’t come back, or rather by evicting biofilm from the tank by throwing it over the side. If the mechanical disruption from the centred airstone isn’t sufficient to keep the biofilm in check, the usual way of removing biofilm is with a skimmer, but that’s another piece of complicated kit to have in the tank which isn’t entirely shrimp-safe and you don’t get the benefit of additional oxygenation (as much?).
The shrimp don’t seem to have noticed or cared about the relocated airstone yet. I’ll update on the effectiveness of biofilm prevention, any residual flung-out water/mess and any emerging shrimp behavioural changes as the new set-up settles in.
Two week update: airstone in the middle is working
It’s been two weeks now since relocating the airstone to the middle/bottom of the shrimphaus and the airstone is working great. There has been no sign of biofilm formation and no more mess flung outside the tank. It seems the mechanical surface disruption is preventing biofilm formation. All together, I’m really pleased with how this worked out. I also found a piece of slate to keep the airstone in place, even though that seemed not really necessary.