oxygen level

Question
I've read a lot that high oxygen levels are good for fish. I have a 30 gallon tank and I was wondering how do you test for oxygen levels and how do you raise them if they are low?

Answer
Hi Matt,

There are tests for oxygen levels out there. They are mostly used by pond and marine hobbyists, but here's a link to one test kit:
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4345+4366&pcatid=4...

If your aquarium were very warm (in the mid to high 80s, the way some people keep discus) that would mean the dissolved oxygen levels in the water would be low. Cooler water has more oxygen - that's one of the reasons why it suits goldfish, and other cold water fish.

Additionally, medication takes oxygen out of the water, that's why it's a fine idea to supply extra aeration while medicating. Also, an air driven corner filter or sponge filter is helpful in a hospital tank to provide extra aeration. Even just employing a few airstones will help to some degree. A very overstocked tank, or a tank with big messy fish, or just a plain dirty fish tank with uneaten food and debris everywhere - will also NOT have plentiful oxygen, because as this organic material rots, it is consuming oxygen.

Unless you have specialized fish, like riverine or hillstream type loaches, I wouldn't worry too much about the levels of oxygen in your tank. In case you do have these sorts of loaches, check out: http://www.loaches.com/articles
They discuss oxygen levels there, and how to make a special tank to suit the especially high O2 requirements of these types of loaches.

Provided your filter is making some splash and disrupting the surface of the water, and your temperature is 75-78 degrees, most fish will do fine with this alone. An addition of a powerhead near the surface of the water (or if you are using an undergravel filter, two powerheads powering the UG filter instead of airstones) will add more water circulation and your fish will appreciate it. Simply put, more water movement = more oxygen, and that's all the average hobbyist needs.

Powerheads are more effective than airstones, but even airstones do help somewhat, just not the way you think! It's not the bubbles that add oxygen, rather it's the fact that it takes water from the bottom and pushes it upward. This mixing helps oxygen to saturate the water. A powerhead is more vigorous, and that's why it performs better.

I hope that helps, and I hope I haven't made the issue too confusing! Feel free to write back if you need any clarification...

Take care,
Nicole