2) Round 2 RTN: You pulled several small levers at around the same time to halt the first event and correct the algae/cyano transition. Poly pad, GAC, Sorb, etc. Taken together -- and in an already compromised state of health -- it may have been enough stress.
^This seems totally possible...
TDS is 0, just replaced the DI resins. Also, the other tanks that are unharmed are running the same exact salt and water (all on the same AWC setup).
I suppose I'm just struggling to understand why it's been one massive event both times... Not one colony here and there, but the MAJORITY of colonies all within 12 hours... I checked for stray voltage, too, nothing...
I don't think there is any rust as the heavy metals can't be detected and realistically could only come from the MP40s, and I looked them over...
On another note, both times the RTN events have occurred, ORP drops considerably. Not sure if this is correlation or causation, just trying to identify ANYTHING that may offer us a clue as to what is going on... There have no been any detectable drops in Alk, Cal or Mag throughout the process, either. Po4 remains at about 0.03ppm, no3 is around 2ppm at most (barely detectable).
Overall it's such a bummer as I do all I can to keep these tanks healthy, and something that I clearly do not know about is killing the stuff I have spent a ton of time and effort into growing... Bummer! I'm really hoping the ATI ICP test may have some insight, as the other two tests provided no obvious clues... You'd think one of the two would detect heavy metals to some degree. Also, the polyfilter doesn't change color, nor does the curprisorb...
I'm too scared to move the surviving colonies into one of the healthy tanks in fear there is some bacteria or other pest/parasite that I can't see with my own eyes that I will introduce to the other systems.... Doing a COVID-esque quarantine on this tank for the foreseeable future.