Dissolved oxygen (DO) is a crucial component of our trout tanks.  Trout and other salmonids prefer cold water because they require high levels of dissolved oxygen, which cold water can provide.  
DO is also a limiting factor for nitrifying bacteria - the more Oxygen available, the better your biofilter will do its job converting ammonia to nitrites then to nitrates.

Below are some thoughts about how to assess dissolved oxygen in your classroom tank.

From David Kline, PA TIC teacher.

The temperature of the water affects how much dissolved oxygen (DO) can be held in the water, but it does not indicate how much DO is in the water. The only real way to test this is with

• a DO Sensor/probe (like a Vernier Lab Pro unit - that is properly calibrated),
• with a Winkler Tititration method test kit, or
• a Chemetrics Vacuette colormetric test kit.

If you have a bubbling airstone, and a working bulkhead with a little air mixed in, then you most likely have good dissolved oxygen levels. It is good to have a kit that tests DO for comparison with your local waterway that you are monitoring/releasing the trout into later.