I was in a similar situation myself here, tank roughly a year old, 80ppm nitrates, I didn't bother measuring the rest. I started dosing nopox, and it took about 5 to 6 weeks to drop significantly. On week 5 or 6 ( I can't recall now ) I was down from 80 to somewhere below 20. I use the API test strips, so getting an accurate reading isn't really possible.
Some rough stats on my tank are, 75 gals of total water volume, 2 clowns, 2 green chromis. CUC is 7 or 8 hermits, some other snails. I do have a really large population of stomatella snails, and by this time the tank has a BILLION (ok it's not that many) of the mini brittle stars.
I guess my point of sharing this is, that I didn't really see any results until near the end of the 6 weeks, and it all came at once. And keep in mind this is anecdotal, I didn't write any of this down or anything.
What I'm more interested in myself, is what causes this condition to begin with. In looking at pix of your tank, you're far more fastidious than I am. My theory is that when the worms and pods start to expand in population, you get more ammonia in your tank (of course), well, this is a self fueling cycle, when you grow coraline or feed, it's going to contribute to their growth, which is going to fuel the cycle. If you're NOT carbon dosing, the likelyhood that you're going to produce nitrates seems higher, so guess what? High nitrates. How do you get rid of it? Short of removing all of the worms and pods, nothing. Water changes don't do it, that's for sure.
Keep in mind, this is just a theory, and I've been lurking here on RC for some time now, and haven't seen anyone else put this forth. So it's possible I'm a crackpot. :fun2: