I flushed with straight water and 1x bucket volume, then immediately followed with a low strength solution and a lot of run off. That fixed the toxicity.
Somehow my nute concentrate had started growing mold (bacteria?) on top, and it caused my TDS meter to read way too low. I got new nutes, an HM TDS/EC meter and calibration solution. That's when I learned my cheap TDS meters had been reading way to low! Now I have the HM tds and a very good ph meter.