Adding more data (maybe it'll help someone else).

Got a handy-dandy EC meter recently and hadn't used it. Thought I'd try an experiment and measure the EC going into the coco and again coming out. Meter shows 240 on the tap water here and after being run through the coco once, it reads about 400-405. Rinse the soil out for a minute or two (did this with my dead plants) and it dropped to about 270. I don't know much about EC, but this doesn't seem unreasonable to me. <shrugs> Need to read up on that more.

So far, it looks like a lot of people "prep" coco coir with CalMag and everyone suggests washing it first.