I kind of figure this has something to do with the fact that cardinal tetras ARE one of the most delicate tetras to have...however, over the past couple of days, 2 to be exact, I've lost...3 of the original 6 that I purchased...a much better count than my neons, though...however...I'd still like to try to narrow down some of the stuff...the first one, I really couldn't identify any "symptoms" persay...other than that he may have been extremely weak to begin with. The same goes for the second one that died...I never noticed any symptoms with him, either. The third, though...he had some kind of white stringy stuff hanging from around his mouth/gill area...I kind of figure it was probably some kind of parasite, though I'm not entirely sure what kind...now, I have one that appears to have the same thing, though not as bad...just a white spot on his head...and another one that has "the whirls." The one with the whirls just continues to swim around in erratic ways...he spins as he swims, swims in circles going nowhere, etc. I've already treated the tank with Naladin for this particular case, as it was suggested I do anyway with all of the tetras since they are rather prone to the disease. Anyway, does anyone have any idea of what may be going on or something? I've tested every possible thing I know to test in the water, and all the tests come out perfect...no high ammonia levels/nitrate levels/nitrite levels, a PH of about 6.8 to 7.0, the temperature stays about 75 to 80 degrees, and there's plenty of oxygen going to the tank. I just don't know what's going on, other than the simple fact that they are cardinals and are extremely delicate...