Well, I know it’s anecdotal but this appears to have worked pretty well.
I added an achilles with no visible signs of ich, to have it appear as if it had velvet a week later. I ruled out velvet, as only my blue tang had a handful of spots, and my Naso, Orange Shoulder, and White Tail Bristletooth tangs had no signs of ich. Additionally, non of my other fish had ich.
At this point, my achilles would not eat anything and had a sunken stomach and very visible spine. Within a day of implementing the DE filter, the ich had visibly thinned out, appearing to have been roughly halved. I continued to run the DE for the next month, recharging as necessary. With each couple days, the fish appeared to get better with less spots.
Not long into the DE running, the achilles began to eat nori with the other tangs. I started soaking the nori in selcon to get additional vitamins to the achilles, which probably helped in its recovery. I continued the selcon for a week or two after stopping DE, still feeding nori for the tangs daily. The achilles still had a few spots at this point, but was visibly more active and squaring off with other tangs for territory. I was pretty confident he had made it through.
He is still doing great, having no signs of ich until I did a major tank cleaning this weekend. I have the DE filter ready to go should it be needed, but he is eating nori and frozen now like a pig, also constantly picking at rocks and trying to assert dominance with tangs more than twice his size.
While I understand one persons experience does not translate to fact, I remain cautiously optimistic that this method of ich management could continue to support my husbandry goals, and could be beneficial to others.
I will do my best to answer questions, should any arise.