Thank's for taking time to reply, Tom! Good to hear that You dont think I'm crazy when I see that more dosing could be needed, thanks!

BTW, I have high Ca (more then 500 ppm), high Mg (over 1500 ppm) and over 16 dH in my tank (hard water from the tap plus this stuff in the synthetic salt). Could the aforementioned "nutrients" - Ca, Mg and KH - supress the uptake of NO3? Or maybe promote it?

What do You think?