Gas bubbles and cardinal tetras

[Frogmouth Catfish]

Having a rather weird problem with my cardinal tetras, as they appear to be getting gas bubble embolisms due to water changes. Lacking an appropriate sink I'm using buckets filled from the bathtub and pumping the water into the tank with a small aquarium pump and tubing. I've tried leaving the water overnight, starting with warmer water, and making sure to break the stream against the surface of the water, but for some reason the oxygen (or whatever is causing this) in the water seems to remain so saturated as to be giving them the aformentioned gas bubbles--they're pretty hideous and I feel bad for them, but its the fastest method of water changing for me. Interestingly, nothing else in the tank is affected--glass fish, cories, loaches, gouramis, SAEs, and others all suffer no ill effects. Any ideas for how to un-supersaturate my water before adding? Airstone overnight? Hydor wavemaker? Something else? Thank you for any input, folks.

[MickS77]

A bubble on a Cardinal Tetra sounds like Dermosporidia/Dermocystidium to me. Not a lot of information out there on treatments. A picture of the fish would be helpful. 

[Frogmouth Catfish]

I'd never heard of this before, but upon googling it seems plausible. My phone takes poor pictures, but I'm noticing some of the bubbles have a small white twist in them that could concievably be a protozoa. What do you think?