Well I'll grant that it's possible there is some growth going on here, although I don't think it is. That's why I'd really love to see the OP scrape off some samples from a few spots and do a little testing on it
Everything posted here so far looks exactly like other cases of plasticizer that I've seen in the past, and I haven't seen anything yet that makes me think it's more likely to be algae. But I could be wrong.
Regarding the tubing, it's possible for different batches to have slightly different characteristics, and I don't think Primochill claims that it's absolutely guaranteed to be 100% free from plasticizer issues to begin with, just that it's much better than their previous tubing. And there might be something in the chemistry of this particular loop which we haven't identified yet which is making it worse than average. It's also possible the tubing he bought was mis-labelled and was the older Pro version with it's well-known plasticizer problems. So I'm not convinced that it can just be flatly ruled out based on reputation alone.
And I think it's entirely possible, in fact common, for plasticizer to look different in different spots. A few causes off the top of my head would be mixing with other impurities, interacting differently with the different materials it's deposited on in different locations, and different levels of aeration as it accumulates changing how it looks.
But like I said, I could be wrong and maybe there is something growing here. I would actually love to see someone get documented proof that their tube or res sludge is in fact algae or some other microbe. I've never seen such a case yet however, compared with many other instances where it was shown to be plasticizer.
One thing that is widely and firmly established science however, is how silver works as an antimicrobial. You're just wrong on that one my friend. The silver coil releases ions into the liquid, because that's what any pure metal does when it's in water. Then the silver ions kill by interfering with cellular respiration as well as other processes.
You don't need for there to be a physical coil at all, all you need is dissolved pure silver for it to work. I suppose it's possible that if you let the loop stay stagnant for a long time, the ions might eventually settle out to the bottom of whatever tube or block they were in, but I think it would take a really long time since there are other forces at play that would keep the ions suspended.