F.A.Q.'s About pH
Q: Why do I need to my pH electrode wet?
A: All glass electrodes have a bulb which must be kept hydrated and a reference junction which must be kept wet to prevent excess leakage of the internal electrolyte solution from the reference junction.
Q: What should I store my pH electrode in?
A: Ideally, storage solution since it has the same chemical make-up of what is in the electrode itself, but if that is not available use buffer 4 or 7 solution. NEVER STORE IN PURE (DISTILLED) WATER!!! In the case of electrodes that are continuously immersed, storage is not an issue since they are constantly wet.
Q: What if I see white crystals on my electrode, what are they and what should I do?
A: It is simply electrolyte (salt) and by soaking the electrode for a couple of hours the electrode will be fine unless it has been dry for long periods of time.
Q: What is automatic temperature compensation (ATC)?
A: Temperature affects pH, yes, but compensation is not to change the reading per se. In fact, ATC is to correct for the effects of temperature on the electrode which would otherwise cause faulty readings.
Q: Are 1.5V batteries OK for HANNA testers?
A: Yes, they will work the same as 1.4V.
Q: How often should I calibrate my meter?
A: It can vary. However, by performing periodic checks with fresh calibration solution you can determine when and how often calibration is necessary.
Q: How should I maintain my pH electrodes?
A: Periodically clean your electrode with mild acid or professionally formulated cleaning solutions and, of course always properly store your electrodes.
Q: How long will an electrode or meter last?
A: Electrodes can last up to 2 years if properly maintained. Meters can last many years if properly taken care of.
What is EC?
Electrical Conductivity (EC) is defined by the ability of a solution to conduct an electrical current.
What is TDS?
Total dissolved Solids (TDS) is defined as the amount of solids dissolved in a solution.
What is their relationship?
The relationship between the amounts of solids such as salts found in fertilizers is directly proportional to their conductivity, therefore, the higher the amount of solids the greater the conductivity. This is because when fertilizers are dissolved into water they become "ions", which means that they become positively or negatively charged and can therefore conduct a current.
How does an EC/TDS meter work?
Two electrodes with an applied AC voltage are placed in the solution. This creates a current dependent upon the conductive nature of the solution. The meter reads this current and displays in either conductivity (EC) or ppm (TDS).
Conversion Factors
TDS meters read the conductivity; the meter automatically converts this value to TDS which is typically displayed in ppm.
Temperature Compensation
Temperature affects the activity of the ions in solution but does not affect the concentration, therefore meters with temperature compensation correct for this condition.
F.A.Q.'s About EC/TDS
Q: How is TDS measured?
A: By means of a conductivity meter. The conductivity is measured and the TDS is calculated by a fixed mathematical formula in the meter.
Q: What about conversion factors?
A: Research has shown that a conversion factor between .64 and .70 to be the best indication of Total Dissolved Solids in growing applications.
Q: Do I need to keep the electrode wet?
A: No.
Q: How often should I calibrate my meter?
A: Typically not as often as a pH meter since there is no junction open to the outside. It is best to perform periodic checks with fresh calibration solution to determine when calibration is necessary.
Q: If I have a TDS meter with a 0.5 conversion factor how do I convert to the correct 0.7 value?
A: Multiply by 1.4; ex: 500 x 1.4 = 700.
Q: How about the opposite situation?
A: Divide by 1.4; ex: 700/1.4 = 500.
Q: What is the difference between microSiemens (µS) and milliSiemens (mS)?
A: Both are units of conductivity. 1000 microSiemens (µS) = 1 milliSiemen (mS).
Q: How do I convert between milliSiemens (mS) and ppm?
A: Convert to microSiemens by multiplying by 1000. Then multiply by 0.7: ex. Your reading is 2.14 milliSiemens (x 1000 = 2140 microSiemens). 2140 x 0.7 = 1498 ppm. Or simply multiply by 700. (2.14 x 700 = 1498)
Q: What if I want to switch to EC measurements?
A: If you do not have a meter which reads both in EC and TDS you may prepare your fertilizer solution according too the directions given and take the EC reading. This will be your value. Or, consult with the manufacturer of your fertilizer for the correct EC readings for that particular fertilizer.
Selective Ions
Nitrogen
Nitrogen is an indispensable element for plant life and a key ingredient in fertilizers. It is present in proteins, vitamins, hormones, chlorophyll, ect. Nitrogen increases the production of foliage and fruits. An excess of Nitrogen can lead to a decreased resistance to disease.
Phosphorus
Phosphorus contributes to the formation of buds, roots, blooming and lignifications. It is also an important component of plant’s DNA and RNA. A lack of phosphorus results in slow growth, smaller fruits and a lower expansion of the roots.
Potassium
Potassium plays an important role in many physiological activities such as the formation of carbohydrates and increases the size of fruits, enhances flavor, has a positive effect on the color and fragrance of flowers. Potassium also makes plants more resistant to diseases.
Dissolved Oxygen
Roots must be properly oxygenated in order to avoid serious problems including water stress which leads to wilting, blossom-end rot and root rot itself. Main causes of oxygen depletion include the formation of a large root mass developing which will impede the flow of water and result in water stagnation. Testing of Dissolved Oxygen is recommended because the problem can start to occur unnoticed and have seriously detrimental consequences on the plant.
Probably one of the most frequent questions we get asked - and there isn't an easy answer we can give. With use pH electrodes drift and as a result you will need to recalibrate your pH meter to the electrodes new characteristics. By and large it depends how accurate you need your pH results to be as to how frequently you calibrate - if you need 0.01pH accuracy then you'll be calibrating every day, if on the other hand you are only interested in 0.1 of a pH or even less, then you need not calibrate that often.
Most of the Hanna pH meters work in the same way but you should always check what your manual says. A general overview of the calibration procedure is present here.
Place the instrument into calibration mode either by pressing the CAL button or pressing and holding down the ON/OFF button until CAL appears on the screen.
At this point most meters will request the use of Buffer 7.01, and all meters will need to be calibrated to pH 7 buffer first.
Place the electrode in to the buffer 7 solution so that the bottom inch of the electrode is submersed. Hanna meters are programmed to automatically recognise a selection of Buffers (please check the product specific specifications to find out which solutions).
While the meter is waiting for the reading to stabilise a clock symbol or hour glass symbol will flash (on some of the hand held meters the reading will flash). If the meter is unable to recognise the Buffer the message WRONG will appear on the screen.
Once the meter has reached a stable reading it will automatically calibrate itself. The meter will then request the use of the next buffer solution, the screen will now show ‘USE 4.01’.
At this point remove the electrode from the Buffer 7 solution and rinse it under tap water (or deionised water) and then place the electrode into the Buffer 4 solution.
Once again the meter will show that the reading is stabilising by either flashing oshowing an hour glass/ clock symbol.
How long a pH electrode will last is dependant on a number of factors. How suitable the particular electrode is for the task in hand, how extreme the chemicals it is exposed to, frequency of measurement and care and maintenance of the electrode. Typically, a general purpose electrode being used to measure pH of water could be expected to give between 1-2 year life, although we have known electrodes go on for many more years than that. An electrode continuously monitoring swimming pool water, on the other hand, might only last 18 months.
Even shorter electrode life can be experienced if the substance is particulary agressive, or if the temperature of the solution is particulary high. In both of these cases careful choice of an electrode designed specifically for that purpose will result in much longer electrode life.
As you will see on our website, we manufacture a wide range of buffer solutions for a variety of applications. However, for 99% of the time buffer 7 and buffer 4 solution are the two you need to perform a calibration. If you are measuring mostly in the alkaline scale, then you might use buffer 7 and buffer 10, although buffer 10 is not as stable a solution as buffer 4, and therefore has a much shorter life once exposed to air.
Apart from rinsing the end of the electrode in water, the best way of making surethe electrode is properly clean is to use one of our special cleaning solutions. Wehave cleaning solutions for specific applications, for example our protein cleaningsolution is ideal for anyone taking pH measurements of food products, whilst our oil cleaning solution will remove oil and grease deposits from the measurement bulb of the electrode which would slow response time down:-
HI 7061 General purpose cleaning solution.
HI 7073 Protein cleaning solution
HI 7074 Inorganic substances
HI 7077 Oil and fat cleaning solution
In order for a pH electrode to give the best response time and accuracy, the measurement bulb of the electrode needs to be kept hydrated. The reason for doing so is to keep a constant ionic presence and keep the bulb of the electrode 'charged' and ready for use.
The ideal solution for this is Hanna storage solution, which not only keeps the electrode at the optimum ionic level, but also inhibits bacteria and algae growth. If you don't have access to Hanna storage solution then you can use tap water (change it every couple of days), or buffer solution. The one solution not to use is distilled or dionised water - as these contain insufficient ionic activity to maintain the electrode and in effect slow it down and stop it working!
pH is a critical parameter for an incredible number of applications going from general water to food, soil, fruits & vegetables, blood, synthetic products and many others. For that, manufacturers have developed different pH sensors for all major applications. This ensures ease of use and longer life of the electrode in a specific application. Different types of junctions, electrolytes and materials used in electrode construction are also part of the design. Below are typical tips and their intend :
Sphere tip: it is the most common tip found in the market as it is mainly used in laboratories on general liquids.
Cone tip: its shape allows easy penetration into semi solids, emulsion solutions, cheese and meat. Mainly used in the food industry.
Flat tip: its construction in intended for surface measurement such as fruits & vegetables skin, drops of samples, human skin, etc.
Knife tip: the knife probe allows for penetration into semi-frozen food, meat, hard to penetrate food products or others. Many other types of tips are available. The above are the most common.
Over time, the junction which is the most sensitive part of the pH electrode can become clogged. This results in the electrode response becoming increasingly sluggish and eventually impossible to calibrate. With the new Hanna replenishable junctions, by using an ordinary pair of tweezers, simply pull out 1-2mm (1/8’’) of the fiber junction and you will literally have a reconditioned pH electrode. This procedure can be repeated up to 15 times, before the whole fiber gets out.
Conventional electrodes are normally single junction. These electrodes have only a single junction which serves to put the reference electrode system in contact with the sample. Under adverse conditions e.g., high pressure, high temperature, highly acidic or alkaline solutions etc., the positive flow of the electrolyte through the junction is often reversed resulting in the ingress of sample solution into the reference compartment. If this is left unchecked, the reference electrode ultimately is contaminated, leading to complete electrode failure.
Hanna’s double junction system, as the name implies, has two junctions, only one of which is in contact with the sample. Under adverse conditions, the same tendency of sample ingress is evident. However, as the reference electrode system is separated physically from the intermediate electrolyte area, the contamination of the electrode is minimized. This leads to long electrode life. The chances of recovery are also higher if proper maintenance procedures are taken.
Extraction method to measure pH & EC is as follow.
1- Mix 3 oz. of soil with 6 oz. of water
2- Let mixture stand 15-20 minutes
3- Filter liquid into clean cup
4- Measure
Simplify these pH & EC measurement by measuring directly into soil with HI 99121 pH meter & HI 993310 EC meter.
No. ORP electrodes do not need calibration with the meter such as pH. Still, ORP electrodes need to be conditioned prior to use.
When the electrode is new, soak the tip in warm tap water. This will enhance the flow of the reference junction. To check function of the electrode, immerse the tip in ORP solution HI 7021L or HI 7022L. The reading should be +/- 50mV from the value indicated on the bottle.
If the reading is not within the +/-50mV, oxidizing or reduction treatment with HI 7092 or HI 7091 is required. It will also prepare the electrode’s surface and speed initial response time. Since in-line process electrodes are already in a solution, a simple test with either HI 7021L or HI 7022L will show you the electrode’s condition. Should your probe not be accurate enough after conditioning & testing, follow the cleaning procedure.
Platinum sensor: use in oxidizing reaction (above 500mV) such as pools & spas, municipal drinking water.
Gold sensor: use in reducing environment (below 500mV) such as galvanic applications, mining industry (Cyanide).
By taking several water samples and making an analysis of each element in the water and then comparing the results with the EC measurement, a ratio was established:
SAMPLE "X"
Analysis |
EC Meter |
Potassium 50 ppm
Magnesium 45 ppm
Calcium 96 ppm
Chloride 80 ppm
Sulphate 99 ppm
Sodium 120 ppm
Aluminum 3 ppm
Zinc 0 ppm
Manganese 1 ppm
Copper 4 ppm
Iron 2 ppm
Boron 0 ppm
Molybdenum 1 ppm
Phosphorus 0 ppm
Nitrate 11 ppm |
|
TOTAL: 512 ppm |
1000µS |
|
Most samples had a ratio of approximately 0.5 for TDS (ppm) compared to EC (µS/cm). The following conversion factor was then established:
2 µS/cm = 1 ppm
(2 µS x 0.5 = 1 ppm)
From there, TDS meters were built to measure conductivity as usual and then multiply that reading internally by 0.5 to display a ppm reading. |
The process of making an analysis of each dissolved element in water is long, expensive and usually requires experienced people such as chemists. Commercialization of TDS meters allows any user to have a good approximation of dissolved solids at an affordable price.
It is important to know that the conversion factor used for TDS meters is an approximation of what a complete analysis would give in TDS.
More important is the fact that this conversion factor of 0.5 was set from a general water analysis, containing normal values of each dissolved element.
Remove the red and black plastic cap or the membrane assembly. Soak the bottom 1 inch in electrolyte solution for 5 minutes. Rinse the membrane with electrolyte and refill with clean electrolyte. Gently tap the sides of the membrane cap to ensure that no air bubbles remain trapped. Adjust O-Ring inside membrane cap. With the sensor facing down screw the membrane assembly.
The probe is under polarization with a fixed voltage of approximately 800mV. Probe polarization is essential for stable measurements with the same recurring degree of accuracy. With the probe properly polarized, oxygen is continually ''consumed'' by passing through the sensitive diaphragm and dissolving in the electrolyte solution contained inside the probe.
"Err 1" is an error code that signifies that the light flow is reduced. The cuvet should be cleaned with the solution and the tissue designed for this use. If this procedure has not removed your error code, the light source will need cleaning. This should be performed yearly, more frequently if required. The light source inside the cavity should be cleaned with the aid of a cotton swab dipped in alcohol.
The zeroing and the measurements should be done using the same cuvet. Interferences are possibly due to condensation or particles on the cuvet wall. Clean the outside of the cuvet with solution and tissue designed for this use.
The current version of this software is Version 5.0. At this time the software is only compatible with PCs using Windows XP and older and is not Mac compatible. If you have an older version of the HI-92000 software then it may not be compatible with more recent Windows editions.
You can use a 357 or LR44 type battery.
Turn the meter on by pressing the MODE button one time.
Once it is powered up.
Press and Hold down the MODE button.
You will see OFF CAL TEMP
Let the button go when you see TEMP
Now press the Set/Hold button to change °C to °F.
Then press the MODE button twice to return to the measuring mode.
You can use your pH 4 buffer. Just place a few drops of that inside the cap to
keep the electrode moist.
No, never use this for storage it will damage the electrode.
Yes, just make sure you let it defrost in a sink incase the bottle cracked when it froze.
Contact Technical service they can provide you with an adjustment procedure.
Yes, Hanna recommends you calibrate your meter before using it.
The is normal and is just crystallized electrolyte which will dissolve if you rinse the electrode with water.
The HI991404 and HI991405 do not work correctly when you have the digital ballasts. The meters pick up electrical interference or noise from the balasts. We have tried installing a capacitor which made them work with the traditional balasts but this does not work. If you have the digital balasts you need to use the HI981504 model.
