I raised guppies for a lot of years and never used salt. They do prefer water that is a little harder, but as long as I had a good strain, mine did fine in softer water too (way back when when I had it. lol). My blue and black moscows always bred very true. That may be strain specific, but I can't recall ever having an offspring that was the wrong color. The color was slightly deeper on some than others, but never a different color. I only culled for deformities personally. I sold the nicer ones online or through local fish clubs (or kept as breeders), then sold the ones that weren't as intensely colored or whose fins weren't quite as big/full to the local fish store.