I have used one for a number of years. What it measures is similar to what a conductivity meter registers. But first, pure water is a lousy conductor of electricity. What changes this is based on what can be dissolved in it. Of this, only what can conduct electricity matters. Hence the term conductivity meter. How this works is simply it has two electrode on one end. When they are submerged in any liquid and a button is pushed it sends out a small electrical charge from one of the electrodes in the direction of the other electrode.
The difference between what was sent and what was received is known. The more that makes it the more conductive the liquid is. Phew!
What a tds meter is inside is a conductivity meter. But once it gets the information on the conductivity, it then uses a formula to convert that into TDS.
To convert electrical conductivity in
microsiemens per centimeter (μS/cm) to Total Dissolved Solids (TDS) in
parts per million (ppm), you multiply the conductivity value by a conversion factor (K) that typically ranges from
0.50 to 0.70. [
1]
Common Conversion Factors (Scales)
Because TDS meters do not measure dissolved solids directly—they measure electrical conductivity and estimate TDS—different industries and geographic regions rely on specific standard multipliers: [
1,
2]
- 0.50 Factor (NaCl Scale): Based on a pure sodium chloride solution. This is the most common default setting for drinking water and general testing in the United States (often called the 0.5 scale or 500 scale).
I used a continuous monitor on one tank where I altered parameters. It offer options and I could choose conductivity measured in microsiemens or TDs/ I had the option of choosing one of two conversion factors and I chose "500."
I used the TDS part of the readings to let me know how close the tank was to the desired parameters which were lowered from my tap and then the water was stained. The pH was targeted to be 6 or a but lower and my tap was 7.0. Long story short, the tank pH tended to drift upwards over a week towards 6.5. So I wanted to move it back to about 6.0. Knowing the params all the time made the job easier. I used pure water mixed with my yap for changing water. I batched it in a trash can next to the tank and just moved the probes into the trash can for that.
I was using the TDS readings to know what I needed to add because most of it wpuld add to the TDS reading. I knew what chemicals I had and might use and how they should effect the TDS. Because I knew what I had and then what I needed, I also knew what should have a fairly immediate effect on readings. This meant I could make the new water pparams where they needed to be. And then by returning the probes to the tank For the refilling, I could see the effect the new water was having as it was going in.
My readings covered almost all the things dissolved in the water, but they told me nothing specifically about what all of them were nor in what amounts. But, the way I used the meter it told me what I needed to know to keep a few of the parameters in a good range for the Altum angels in the tank.
Where it helps, as noted in above posts, is when it is an indicator of changes. Hower, we need to shave some idea of what is likely cause the the changes for the information to be the most helpful. Our tank water is not naturally stable. Some things get used up and need to be repelnished. Other things build up and need to be removed. That is the main reason we do water changes. A TDS meter can be used to alert us to changes in a tank and then we may need to do some sleuthing to figure out what is going on. We also might not succeed at this.
As for how usefull your specfic readings are, it depends on what is in each tank. Inhaitants, decor, plants and maint. routine all can cause changes as can feeding, fertilizing etc. dechlorinating etc. I assume yo might be cycling these tanks? If so ammonium, nitrite and nitrate can all effect conductivity/TDS. Unless to have some very exact measurements of the true amout of water in each tank and then the exact ml of ammonia you are adding, and then that your are adding the ammonia at identical ppm lebels and ebrything else in the tnks is proportionally thrsame that can explain the difference between the two tanks and both to the tap, But the 80L is pretty close to tap and the 5 is not all that far either.
