As title says, my male guppy has developed a black spot, and I'm not sure how or why, and possibly a second one. I'll enter all pertinent info and include pictures below:
Tank size: 10g
pH: 8.0 (very hard city water)
ammonia: 0
nitrite: 0
nitrate: 0.12ppm
kH: unknown (but I know it's full of...