This may sound silly, but have you run a phosphate test on your RODI water? I saw that you used a TDS meter, but did you run a secondary test checking specifically for phosphates? Sometimes the TDS meters don't pick up as well for it; I had a meter say 0 but there was still phosphate showing up. The iron and copper was out but phosphate sneaks through. City water is also bad for phosphates as a general rule.
Hope you get it figured out! Diatoms and cyano just plain suck and they make a tank look awful real quick. I hated my own fight with the stuff.
Hope you get it figured out! Diatoms and cyano just plain suck and they make a tank look awful real quick. I hated my own fight with the stuff.