You can run these tests at home with the right gear. There are several test kits available and all are pretty affordable.

Oxygen is the final electron acceptor in the respiratory metabolism of the animal cell as conducted at the level of the cells' intracellular mitochondria. That's about all I know about it from memory.  Oxygen is soluble in water but not very well. Oxygen may rane from zero PPM up to a glorious 14 PPM. There are a range of concentrations which have different clinical presentations:

• 3 PPM = Fish are dead and dying
• 5 PPM = Fish are extremely lethargic. Ammonia is even more toxic at this level. Appetite is reduced or absent.
• 7 PPM = Circulation and surface exposure of water could stand improvement. No fish will die unless something else impairs the gills or binds more oxygen (Such as Formalin application).
• 8+ PPM are desirable
• 11+ PPM are gloious. The hobbyist with this has dancing, playful fish.

But how could you know what your dissolved oxygen is? Well, there are chemical tests. One comes from Hach Chemical Call them at 800-227-4224

The diagnosis of a low oxygen condition is not as simple as you might think. Of course, if you have test kits or a testing pen, you're fine. But the problem comes when folks see a gasping fish and assume that there's an oxygen deficiency when indeed the fishes' gills are "shot" due to pH crash or some kind of parasitism.

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