Platies have been domesticated for so long that they are very tolerant of water chemistry. My favorite fish reference is Seriously Fish http://www.seriouslyfish.com/species...rus-maculatus/
Temperature: 68-79°F (20-26°C)
Hardness: 10-30 dH (160-530ppm)
"As long as the ph remains above neutral this fish is one of the best species available to the beginner."
I keep three color varieties of X. maculatus
and I never worry about water chemistry, but my tap water is relatively hard and always well above pH 7.0. On the rare occasions when I have tested the water, GH was 150ppm, KH 160-180ppm, and pH 7.8.
I'm glad to see another platy fan on the forum!