Is there scientific proof that the opposite poles of a magnet have different effects?

Question

I placed the north (geographical north) pole of a magnet towards the side of a fish tank (which needs cleaning) & left it there for approx 12hrs (over night). White stuff (minerals? mold?) appeared on the inside of tank covering where the magnet was (a small circle shape). I then did the same thing but with the opposite pole facing the tank and the next day the white stuff had disappeared again. Is this proof the poles of a magnet can have a different effect?

Answer 1

Hardly, have too many other variables here like the composition of both sides of the magnet, insulating properties, and the like. A compound of unknown could be leaching out of the magnet, the opposite pole could be retarding or reflecting a light from outside the tank. These are but a few.

This is just a start, one would need to isolate all variables that might cause this effect. In particular, find out of the Mold, or mineral stuff might be attracted or repelled. Gather some and find out.