Hi all,
but feel the best way to progress with growing aquatic plants is to understand and monitor the chemicals and see how these levels effect different plants.
It would be good, the problem is that you need a lot of different kits and meters to actually get accurate results, and the tests and kits you need can vary dependent upon how hard and "salty" your water is.
I had a go at this a couple of years ago, mainly because some of the tanks are in a lab. next to an analytical lab., and I asked the technician to run a tank water sample through the AAS, ISE etc. when they had a run of water samples to analyze.
This gave me a datum to work from. The outcome was that it is quite difficult to get accurate, repeatable values for parameters like NO3-, even when you have Ion Selective Electrode (ISE) etc.
There are techniques that can give you more accurate readings for some parameters. You can get more accurate pH readings in very soft water by adding a neutral salt (usually NaCl), but if you have very soft water pH is going to be inherently unstable anyway. Conversely if you have very hard water you know pH will be ~pH8 and it really doesn't matter what you test it with, it will give you much the same value.
An atomic absorption spectrophotometer (AAS) will give you accurate and repeatable values for metals like potassium (K), magnesium (Mg), calcium (Ca) etc. but the results may still need interpretation. If you're a plant there may be no difference in response between 5 and 50 ppm calcium, but there might be a huge difference in response between 0.5ppm and 5ppm Ca, and these critical values will vary from plant to plant.
I eventually settled on the <"
Duckweed Index">, basically a colour and growth index of a non-CO2 (or light) limited plant and an optional conductivity measurement, because it is actually a much more sensitive metric than using test kits.
cheers Darrel