By Frank Cowherd
A TDS meter is a great tool for any fish room. TDS is total dissolved salts. Basically, it measures metal ions like sodium, potassium, calcium and magnesium. All of these metals are dissolved as ions in the aquarium water. Usually sodium is part of sodium chloride but could be sodium nitrate or sodium nitrite or sodium phosphate or sodium silicate. The same is true for all the other metal ions. The meter only metal ions that are dissolved, so it metals are part of the solids in the tank. The meter actually measures conductivity, the amount of current that can pass through the aquarium water and the read out on the meter is in ppm and is calculated as if all the ions were sodium chloride.
So what can you do with such a meter in your aquarium? I basically use it to determine when my black water aquariums need to have a water change. I generate RO water which the TDS meter says has less than 10 ppm salt content (the actual number is usually 6 or 7 or 8 PPM). I use this number to confirm that the RO unit is still generating good water. If the number is high, I know it is time to replace some item associated with the RO unit. Then in my 7 black water tanks I allow the TDS to go up to 150 ppm. When the TDS hits 150 or close to that, I do at least a 50% water change. However I prefer to do enough of a water change to get the TDS to read 30 +/- 5 PPM after the change. The PVAS raffle will have one of these meters in the monthly auctions every other month. SO you have a chance to win one of these meters if you buy a few tickets at the monthly meetings. SO what can you do with a TDS meter? I'd like to hear what other have been doing with the TDS meter?