[UniQuaria] bristle nose pleco question
There are actually test kits specifically for oxygen if you want to go that route. Here’s a site that carries them, so I’m sure there are many others:
http://www.aquariumguys.com/oxygen-test-kits.html
I don’t know anything about this company, just grabbed one of the first links that came up on Google so I could show you what I mean. 
In the past, when I observed this behavior, I made sure filters were working properly (on the tanks I used them on anyway) or that my plants were getting proper lighting and putting out tiny air bubbles. Sometimes when fluorescent lights start to age, they stop putting out enough light and you can actually watch the difference in the plants. Or if you are using CO2 injectors or the like, a drop in daytime O2 levels could indicate a problem with that system. Not knowing how your tank is set up, I’m just throwing out possibilities.
Dawn T
Category: Philippines Internet Koi Society
