GH at 30 is presumably 30 ppm, which equates to 1.6 or less than 2 dGH. I do not recommend livebearers (like platy) in such very soft water. They may look OK now, but I can assure you they willnot live a normal lifespan because of the lack of minerals which they need. Here is some reliable info on platy:
Originally Posted by BubblesBunny
You will have healthier fish if you select soft water fish. It is always esier to have fish suited to your watedr, rather than trying to adjust the water for fish, though that can be done.
Byron Hosking, BMus, MA
Vancouver, BC, Canada
Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]