Hydroponics Supplies: pH Test Kits
It's been established that the most optimal pH for hydroponic growth is around 6.0, although a larger range, 5.0 to 7.0 is tolerable. This optimum is slightly more acidic than the pH optimum for top soil (around 7), because in lower pH there is a better solubility of some salts (such as calcium phosphate) and also lower pH discourages bacterial growth.
There are three methods available for checking acidity of solutions. Electronic, using a pH meter, or relying on pH-sensitive dyes either in solution or incorporated in paper strips. Generally, the most accurate method is using a pH meter, freshly calibrated with at least two reference buffers. This method, however, is not working very well when used to check pH of hydroponic media because pH electrodes have a very slow and erratic response when very diluted buffers (in a range of 0.1%) are used. The pH indicator dyes, on the other hand, provide instant read-outs with reasonable accuracy. Paper pH strips are most convenient but the least accurate. Their accuracy (±1 pH unit) is on a borderline usefulness for hydroponic applications. About twice more accurate and just about as quick and simple are some pH indicators in solution. Wide range pH testers, easily available on the market, are not the best choice for monitoring hydroponic media as they have accuracy only slightly better than pH strips. Single dyes give more narrow range for color changes, usually within 2 pH units. A very good single indicator dyes that work within pH range for hydroponics are bromothymol blue (yellow at pH 5.9 and blue at 7.7), covering well the high pH range, and bromocresol green (yellow at pH 3.7 and blue at 5.5), covering well the low pH range. Both dyes give sufficiently accurate readings with a 'friendly' for the eyes yellow-green-blue color shift, however, they miss parts of the optimal pHs. Bromocresol purple is the dye seemingly 'created' for hydroponics, with a color change within pH range of 5.2 to 6.8, but with 'unfriendly' colors, yellow-brown-purple, where the transition from yellow to brown is difficult to resolve by the eye. We developed a combination of dyes that cover the entire range of hydroponic-useful pHs, and call it the Best Hydroponic pH Tester. It provides easy to distinguish range of colors, from red to dark green within pH range of 4 to 8, with 0.5 pH unit accuracy. All the dyes are available from this site. Click on:
Best Hydroponic pH Tester
to see the basic information about them and how to order.