This pH Control Kit by General Hydroponics includes everything you need to check and maintain the proper pH levels for your indoor garden. 

It's easy to use and covers a pH range of 4.0 to 8.5.

To use the ph Control Kit, fill the test-tube halfway with nutrient solution, add a few drops of pH Test Indicator. Check the resulting color against the color comparison card to find the pH level. When the pH level is too high, slowly add pH DOWN to reach the desired level. When too low, of course, add pH UP.

As a general rule of thumb, red means the pH is too low (acidic), blue means the pH is too high (basic or alkaline), and yellow to yellow-green is about the correct pH level for most gardens. Different plant species may need different pH levels, so be sure to adjust according to your crop.

Includes:

8 oz. pH UP
8 oz. pH DOWN
1 oz. pH Indicator Solution
Vial for testing
Color comparison card