So I've had my aquarium for almost 3 months now. Today I did a cleaning, gravel vac, water change, snail thinning....and before I could finish my entire arm that I was sticking in the water was red, burning and covered in hives. I am definitely prone to allergies. This is the 4th time in the past month I've had allergic reactions, however, this is the first time it's happened during a tank cleaning. Has anyone ever heard of such a thing before? Any ideas what it could possibly be that is triggering the reaction? I didn't test the water prior to the cleaning, but my readings have been 0 ammonia, 0 nitrite, less than 10 nitrate and ph 8.0 for the past 2 1/2 months.