Not exactly the same characteristics. Water that runs off the land and goes to a river won't have much hardness to it while water from a well that had been filtered through a limestone layer will be considerably higher in GH
. 300ppm is considered to be high GH
but it's still perfectly fine. I keep and spawn discus, rams, angelfish, and others in the same exact hardness (from a well) and the eggs are fertile when they aren't supposed to be. I really wouldn't worry about it. If it bugs you that much you can change it with some purified water or do a 100% water change with your tap water, which I'm assuming is at 75ppm since that's what you stated it started off as.