Your question must have fallen thru the cracks. Yeah 300+ is a little high ppm for clean water. You need to reverse osmosis it down to under 50.

The second question is often misunderstood. The high ppm in clean water is from calcium magnesium and other elements. When they say to put in 200 to 300 ppm they are referring to NPK; your base nutes. Next throw in a teaspoon of CalMag per gallon irrespective of how that effects your ppm (Hint: it will go heigher).

Last, enjoy!