I, like many others on this forum, do not really like the phenol ed method of measuring pH. In this light I had been looking for an electronic pH meter with the right combination of price and accuracy. There are many pH meters at low prices, but offer poor accuarcy (~0.1 pH). Recently I found one that offered a good price (under $40) and good accuarcy (~0.03 pH). This unit is the model PH-903 from ZD Instruments, shown here. You can find them on eBay by using the seach term "ph meter 0.03".
Product Description
This pH meter is a small hand held unit similiar to a small stick. It is rectangluar with the probe at one end. The probe is covered with a cap when not in use. This keeps the probe from drying out. In the middle of the unit is a on/off switch and an LCD display. The top of the unit is removable and holds four small disc type batteries. The meter comes with a black leather case (for me useless) and an adjustment screw driver. To take a pH measurment, press the on/off button once to turn the unit on, remove the endcap and place the end in the liquid to be tested. Reading stabalizes in about 5 to 10 seconds. Remove from the liquid, turn unit off by pressing on/off switch, optionally clean the probe with clean water, and replace endcap. The meter is rated "water resistant" which probably means it will with stand splashes, but not submersion. All openning have gaskets on them.
Drift and Calibration
One issue with electronic pH meters is drift and calibration. This meter has two adjustment points, zero and span. The zero, or pH 7 adjustment is located on the back of the meter under a small cap. The span adjustment is accessed by removing the top of the unit. Calibration procedure starts with preparing two pH calibration buffers. I use Hach power pillows found here. Because pool water should be above pH 7.0 for the span I use pH 10.0 buffers.
After preparing the two buffer solutions, turn the meter on and place the probe in the pH 7.00 buffer. Wait until the reading stabilizes, and if it is off by more than 0.03, adjust to pH 7.00. Remove the meter, wash the probe with clean water and place into the pH 10.00 buffer. Again wait and adjust if necessary.
I have found that drift on this meter is not a big issue. The instrument remains within stated accuracy limits for three to four weeks without adjustment. If you can tolerate a larger margin of error, then probably can go for months without calibration. This instrument is very accurate and easy to use. While not as inexpensive as the phenol red indicators, I like the accuracy and ease of use over them.
Product Description
This pH meter is a small hand held unit similiar to a small stick. It is rectangluar with the probe at one end. The probe is covered with a cap when not in use. This keeps the probe from drying out. In the middle of the unit is a on/off switch and an LCD display. The top of the unit is removable and holds four small disc type batteries. The meter comes with a black leather case (for me useless) and an adjustment screw driver. To take a pH measurment, press the on/off button once to turn the unit on, remove the endcap and place the end in the liquid to be tested. Reading stabalizes in about 5 to 10 seconds. Remove from the liquid, turn unit off by pressing on/off switch, optionally clean the probe with clean water, and replace endcap. The meter is rated "water resistant" which probably means it will with stand splashes, but not submersion. All openning have gaskets on them.
Drift and Calibration
One issue with electronic pH meters is drift and calibration. This meter has two adjustment points, zero and span. The zero, or pH 7 adjustment is located on the back of the meter under a small cap. The span adjustment is accessed by removing the top of the unit. Calibration procedure starts with preparing two pH calibration buffers. I use Hach power pillows found here. Because pool water should be above pH 7.0 for the span I use pH 10.0 buffers.
After preparing the two buffer solutions, turn the meter on and place the probe in the pH 7.00 buffer. Wait until the reading stabilizes, and if it is off by more than 0.03, adjust to pH 7.00. Remove the meter, wash the probe with clean water and place into the pH 10.00 buffer. Again wait and adjust if necessary.
I have found that drift on this meter is not a big issue. The instrument remains within stated accuracy limits for three to four weeks without adjustment. If you can tolerate a larger margin of error, then probably can go for months without calibration. This instrument is very accurate and easy to use. While not as inexpensive as the phenol red indicators, I like the accuracy and ease of use over them.
