Thought I'd post the results of some testing I conducted. This is related to my offers here
I took a sample of water from my betta tank (1.5gal, duckweed infested) before a water change, after a 25% water change and addition of fertilizer and traces, and a sample of the tap water used for the change. I analyzed for Na, K, Ca, Mg, Cl, NO3, and SO4. Here are the results (tap, then pre-WC, then post-WC, in parentheses is the value reported by my municipal water supplier if available)
Na+: 9.5, 23.3, 25.3ppm (16)
K+: 2.5, 22.4, 34.5ppm
Mg+2: 2.2, 3.9, 7.4ppm
Ca+2: 15.3, 16.7, 17.4ppm
Calculated total hardness (GH) from above values: 47.5, 58.1, 73.9ppm (56)
Cl-: 25.3, 50.6, 57.8ppm (20)
NO3-: Not detected, 15.6, 17.0 (0.38 maximum over 1 year)
SO4-2: 51.8, 120.5, 144.9ppm (35)
After the water change I added: a "squirt" of Kent Freshwater Plant, a few crystals of Epsom salt (MgSO4*7H2O), and a few crystals of KNO3.
So a couple of obvious questions: 1. Why is the sodium so much higher in the tank? Well, I looked at the ingredients on the Kent and it contains both sodium-EDTA and sodium molybdate. I assume these are the main sources.
2. Why is the chloride higher in the tank? Again Kent includes muriate of potash which is KCl. It also contains cobalt chloride.
The higher sulfate and magnesium are due to the Epsom salts, while potassium is due to both the Kent and the KNO3.
I'm still trying to develop an easy test to differentiate and measure Fe+2/Fe+3 as well as a better phosphate test. The above was the result of a capillary electrophoresis separation with indirect UV detection.
It is nice to know my tap K+ value as well as the resulting conc. in the tank - it verifies my dosing levels. Also, the nitrate is much more precise than the colorimetric, so no guessing "is that 5ppm or 10ppm?"
Fun with chemistry (and instruments)!
72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias
2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.