Are you filtering the air from outside with carbon that's injected into your skimmer? Just thinking maybe your neighbor didn't spray anything, but the city could have.
I'm also running rox and it's worked well for me at the early stage of my tank. If you do increase the carbon, maybe try and see if the decline changes for better or worse. I know people say rox is really aggressive with Zeovit, so if the decline gets worse, maybe switch over to a different type or reduce the amount further. If the tanks stops or starts getting better, it could something did make it's way into the tank. Worst case is no change at all rough.
I saw you mentioned if you start over you'd go with another nutrient management system, what do you think you'd go with?
Im not filtering the air at all, and our city doesnt spray, but since it can't hurt, I put some carbon in a mesh bag and canister, and added it to the incoming air line just to be safe. I also replaced the carbon in the tank with fresh and put it inside the filter sock (I run a single 7" sock in my set up) for increased exposure. I used 2/3 a cup and replaced with fresh rather than increase the carbon so I maintained at least one parameter of the change. If things get better, I can just replace the carbon every few days, rather than increase and have a chance at going overboard with stripping the water.
As for the nutrient management system - I havent really given this a lot of thought yet. I like ZeoVit, its been relatively hands off and easy to maintain schedule wise. I dont use a lot of "extras" which I think made it nice to prevent things from becoming a "chore". I dont really want to do any kind of refugium - Ive never had much success with them, and they seem to become much more of a mess than I want to deal with - and sump space is already at a premium. I have run Triton before and my nutrients were always much higher in the system as a whole. So that gets rid of most of those systems. Ideally, I would continue to use ESV two part, so maybe something similar to Zeo, a bacterial driven system, but something more like NO4PO3-X or VSV? Im not entirely sure yet. I have to do more research.
I keep thinking that my current issues are exacerbated by the death of the derasa - that clam was probably mopping up a lot of the high nitrates that Im seeing now, and so it was never really a problem prior to its death. Thats not to say that its what caused the acro issue - that was happening before - but if something was already causing an issue, and then there was a big ammonia and/or nitrate spike due to the clam kicking the bucket, it seems logical that the resulting instability would wreck havoc on an already compromised system.
Who knows... maybe this spring, I'll redo the entire tank, when I can afford to have a custom refugium sump built for the tank, and then I can start from scratch - new rocks, new sand, new frags...
I dunno... I feel even worse when I start thinking about that, because I dont want to give up on this guy... hell I set it up almost two years ago to the day