Measuring dissolved O2.

[smidoid]

Or more to the point, HOW do you do it? I always thought that provided the fish weren't all wearing snorkles then there was sufficient 02 in the tank. However, now I read that you can have too little -OR- too much.

There's a surely a happy medium - but how the heck do you test for it?

[Steven Pro]

There are O2 probes/monitors, but I have never used one.

[smidoid]

There are? What's it measured in then? It's 02 sats on ER and House (etc.) but that's blood oxygen, water I presume is different' and different in sea and freshwater too.