I almost never use ny GH kit, I use the KH one for my bio-farm but not my normal tanks. TDS is actually calculated by appluing a formula to conductivity. It is important to understand the basics of water chemistry.
Pure water is hydrogen and oxygen. Put in a conductivity or TDS meter and it should read 0 ppm. But in reality it takes stingent lab conditions to have pure water. More on this later.
Pure water is a lousy conductor of electricity. However, what does make it a good conductor is the other stuff in it. The other stuff conducts the electricity. And this is why a conductivity meter is used to measure the content of water beyond H20. It works by send a fixed amount of electricty between two probes. By measuring how much ot that reached the second probe is how conductivity is calculated.
Unlike GH or KH test kits digital measure will include everything in the water. Dissolved organic matter, mineral, ions. compounds etc. etc. What this measure will not do it to determine what exactly is contributing to the reading. For that other tests are needed and this can be a lot of different things. Ammonium, nitrate and ntrite all contribute to conductivity so do any other ions.
Digital tests can be pricey depending on what is being tested. Further, the greater degree of accuracy one want, the more they will cost. I had two pH hand held meters I threw out because they are pretty crappy. I now have a $250 continuous monitor on my altum tank to measure pH, Temp. and Conductivity/TDS. It is not instant but is quick enough to serve my purposes. When I change the pH I useally wait 5 minutes or more to check the monitor. This is because the test kit vial tests 5 ml of water and the tank is 55 gals. I need to wait for the effects to spread ttough out the tank. It matters where in the tank. I will put some muriatic acid in several places including the opposite end of the tank from the probes. So it takes time to circulate and give me a true reading.
The problem with hobby test kits is they are limited in their range in many cases. I have nor seen an aquarium test kit that read pH under 6.0. Even my probes have trouble with very low pH. Since I keep the tank tea stained. colormetric tests are pretty much useless.
A good friend has a YouTube channel on aqariums. She is a published author and speaker at events. She was sent a decent new digital water testing device Fro API into which one put a water sample and it gave readouts on all the sorts of things we want to know about our water. Here is their description:
Presenting API AQUASPIN, a cutting-edge technology that combines speed and accuracy for the best aquarium and pond water analysis results anywhere, all in just two minutes! Using AQUASPIN is simple – all it requires is a small water sample from your customer, the AQUASPIN photometer and a new disk. The water test (freshwater or saltwater) takes fast and accurate readings of aquarium or pond parameters, including, where applicable, nitrate, nitrite, ammonia, phosphate, carbonate hardness, general hardness, pH, magnesium, and calcium. No need for color comparison or human interpretation, the AQUASPIN technology provides your results accompanied by an API product recommendation all with the click of a button.
Now for the kicker, "
How much is the API Aquaspin?
$1200 + $175 for every 50 discs.Aug 13, 2020
So folks how many of you have $1,200 to spend on testing? or do you want more accurate digital tests? You can spend more than $1,200 for a high qualoity single parameter digitasl tester if you want the greatest accuracy.