No. But it's quite possible that it's coming from THESE:
I stumbled across the remains of these two screws yesterday while moving my Kalk doser off the lip of my sump. As I now recall, they were there to hold a lighting fixture in case I ever wanted to use part of the sump as a refugium. I never did, eventually placed the doser over them and forgot about them. This was maybe 5-6 years ago, before the previous crash.
I'm not about to say just yet that these screws are the only cause, but it is highly probable that through condensation, splashing, salt creep and the like, that they've been slowly dripping all kinds of heavy metals into the sump for a very long time now. I am still persuing other possible contributing factors but everything else (other equipment, incoming water, etc.) is all coming up clean.
By the way, you will note that the nut of one of the screws is missing. I noticed it too. It either was never there or has rusted away completely because I'm positive it hasn't fallen into the sump.
So now, my question to you guys is, do you think that given how long this condition has occurred, it is possible for something this small to be the EXCLUSIVE cause of bringing down a 650g system or should I continue looking for their accomplice? I'd really love to finally put this crap behind me. Thanks.