Perlite adds water retention, drainage & aeration while Vermiculite adds aeration, drainage, root anchorage, nutrient uptake & avoids soil compaction. When combined, they complement each other & create a healthy balanced environment for the crop.
It stands for the power of Hydrogen. The importance of knowing the pH of your reservoir: When the pH of the nutrient solution is out of balance (either too acidic or alkaline), your crops will not be able to uptake the nutrients in the water, basically starving them, even though it is available to them. Solution: use your pH testers to determine the pH level, then add pH adjusters called "pH up" or "pH down" to amend your nutrient solution to the optimal pH range.