It's true but other factors can effect this too. It can lower or raise from plant giving off waste salts. 5.2 to 5.8 is best. Shurely you must have a pool or pet store that has dropper kit to check PH. They are cheap and mind you the color of the GH 3 parts will change the color but you will be much closer than guessing. It's not worth playing with and it can hold you dead still till it's fixed. Get a small kit till you get a PH pen.