OP: If your test was accurate, keep removing things from the tank and placing in RO water until you find the source. To speed the process up, and a little vinegar. The vinegar won't register in the test kit, but the acid (in vinegar) will help dissolve Ca and Mg faster.
Thanks for the links, will read through them.
I like your signature, I recall you using that line in a post you made on one of my threads. Haha
Just to help me better understand, the "vinegar molecules" would "consume" the Ca and Mg into what? Any by-products or just dissipates/disappears?
I assume the pH would lower since the GH would lower and/or since vinegar is acidic. Any effect on KH with the added vinegar? Is the pH drop from the added vinegar safer than the high levels of GH (assuming Ca and Mg)? Any recommended safe dilution ratios of vinegar to water volume?
The fumes/smell of vinegar that dissipates, is that something else off-gassing from the vinegar or is it the actual vinegar evaporating?
Haha, sorry to derail, just curious.
And to OP, audionut's recommendation to set up tests for each item to rule them out, is a good one.