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Frequently Asked Questions

pH Meters

Why does a pH meter need calibration?
The pH probe is a semi-permeable glass membrane with a reference solution inside.  That means, to some degree, that liquid can pass through the bulb in either direction.  Over time, the reference solution changes, and the meter needs to be calibrated.  If the meter is kept in storage for a long time without storage solution, more of the reference solution leaves the probe, so a meter that is rarely used may need calibration more often than one that is used frequently.

Why does Hanna recommend calibrating even a brand new meter?
Hanna QC's all its meters before shipping, but they are not precisely calibrated.  In addition, while the meters are in stock with Hanna or its distributors, the meter is subject to the changes outlined above.  We sell a lot of meters, so you are always assured of fresh stock... the meters in our inventory have rarely been there more than a couple of weeks.  But for lower volume sellers, that's not always the case.

Can I use a new meter without calibrating it?
Of course!  Calibration solutions are important and will be needed eventually for ALL pH meters.  But your new meter will work normally  (although not as accurately), without calibration.

How do I "condition" a new meter or probe?
Let it soak in either pH 7.0 buffer or storage solution for a couple of hours.  The meter does not need to be turned on during this process.

What pH calibration solutions should I use?
The most accurate calibration is done with two points- either 4.0 and 7.0 (if you expect to read acid values below 7.0) or 7.0 and 10.0 (if you expect to read alkaline values above 7.0).  If your readings do not need to be especially precise (just "in the ballpark), you may be able to do just a one point calibration, especially if your expected readings are right around one of the three standard values (4.0, 7.0, or 10.0).

How often should I calibrate my meter?
This can be a difficult question to answer.  If the meter is used regularly or if it's stored properly, you will not need to calibrate as often.  If you need to read pH values precisely, you should calibrate more frequently than if you do not need as much precision.

What if I need to measure pH of sushi rice?
Measurement of the pH of sushi rice has become a big issue raised by local health departments.  We suggest either the HI 98107 or the HI 98127 meters.  As a safety precaution, take some of the rice from the pot, allow it to cool and make a 2 - 1 mixture with distilled water, then read the mixture.  Many health departments require that the meter be calibrated with both 4.0 and 7.0 solutions.

How do I measure the pH of soil?
Standard pH meters are designed to read the pH of water-based solutions, not solids.  To measure soil pH, make a 2 - 1 mixture of soil and distilled water, then read the mixture.  There are some very inexpensive meters on the market that purport to read soil pH directly, but generally they are not very accurate.  Hanna's HI 99121 has a specially designed probe that allows direct measurement of soil. 

Can I read the pH of bio-diesel?
pH meters are designed to read the pH of aqueous (water-based) solutions.  Since most bio-diesel does contain some water, you can get a reasonable estimate of the pH of bio-diesel using a pH meter.

Conductivity Meters

What are "EC" and "TDS"?
EC means electrical conductivity, and is a measure of a solution's ability to conduct electricity.  EC is measured in micro-Siemens or milli-Siemens.  It gives a good measure of the "ionic content " of the solution.  TDS is simply the measure of total dissolved solids, and is usually measured in PPM (parts per million), or PPT (parts per thousand). 

How do I convert from PPM to PPT (or visa versa)?
1 PPT = 1,000 PPM, so if you want to convert from PPT to PPM, just multiply by 1,000 (add three zeroes).  To go the other way, divide by 1,000 (move the decimal point three places to the left).

How do I convert from micro-Siemens to milli-Siemens (or visa versa)?
1 milli-Siemen = 1,000 micro-Siemens, so if you want to convert from milli-Siemens to micro-Siemens, just multiply by 1,000 (add three zeroes).  To go the other way, divide by 1,000 (move the decimal point three places to the left).

You offer several meters with "high" or "low" range of conductivity.  Which one should I get?
You need to find out what range of values you expect to read and get a meter that reads within that range.  In most cases, the high range meter will cover all situations, but if your expected readings fall within the capability of the lower range meter, using that one will give you more precise measurement.

I make ionic (colloidal) silver.  How do I measure TDS?
Colloidal silver is a suspension, not a solution (the silver is not fully dissolved), so you are only getting an approximate measure using a TDS meter, since these meters can only measure what's dissolved in the solution.

General Questions

How do I get technical assistance?
Hanna has an excellent tech service department in their Rhode Island home office. You can reach them by phone at (800)-426-6287, or by email at tech@hannainst.com. Hours are Monday - Friday, 9AM - 5PM EST.