Toward the end of the trout growing period you have a lot of stuff acting against your trout. Your trout are big and make a lot of waste which depletes oxygen as it breaks down, your trout are big and need lots of oxygen, and your weather is getting warmer, and warmer water doesn't hold as much gas as colder weather does.
You can test this by opening a warm can of beer, or waiting a few years and watching what happens when the oceans stop absorbing carbon dioxide as they warm up a bit.
Anyway...
I have a tube dumping water from my growbed to my sump.
It's not under pressure, but is simply overflowing from the growbed at that height. ie this tube's height regulates the depth of the growbed.
no pressure
The tube stopped a few inches above the water and made some nice splashing and bubbling which I thought was adding some oxygen.
I'm probably quite correct in thinking that.
This sucks air into the tube via the Venturi effect.
Apparently, this is because the water experiences higher pressure at the restriction just below the elbow, but then lower pressure when the tube becomes wider again. The result of the low pressure is that it sucks in air.
Which is a little odd.
When you put holes in (or before) the bit that's actually restricted, the holes blow out water.
I know because I checked.
Even more oddly, is that the bubbles don't ever really come out. Some do when the water level is a little low, but these are very small, and not many.
The tube is full of bubbles all in chaos, churning around madly.
The bubbles enter at the top just where the clear tube starts, and they move all the way to the bottom.
Which is also odd given how gently the water is flowing.
At first I thought they were the same bubbles, but if you block the holes, they clear after a few minutes.
Interesting.
As far as I can tell the air is dissolving.
I have no idea if I'm probably quite correct in thinking this.
If gas really does dissolve in water that readily and in that quantity, it's no wonder fish can live in the stuff.
I think I just got re-interested in the world.
Perhaps it's because I stopped taking all those opiates for my hurty ribs.
120 Things in twenty years thinks ribs make me less thinky.
[EDIT FROM THE FUTURE - I Thought I'd add a link to wikipedia's entry on Venturi and now that I've read it I don't think I have any idea what I'm talking about, but what I did clearly works. I'm just no longer sure why]
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