Keeping pH levels correct is one of the most important aspects of indoor gardening. Unlike gardening outdoors, where rainwater and soil provide ample buffers and corrects to input pH, indoor gardens must correct for pH variations in both source water and nutrient feeds. Tap water …can vary in its pH because different cities and municipalities add different chemicals and buffers to keep pH above 7. Nutrients usually have very acidic or alkaline values thanks to the mineral salts or concentrated organic supplements. Different species of plants vary in their pH requirements, but a common rule of thumb for indoor growers is 5.5-6.5 for soil, and 5.8-6.3 for hydroponics. HTG Supply carries top brands like General Hydroponics, Earth Juice, Advanced Nutrients, and Nectar for the God, all with excellent pH Ups and Downs.