I have absolutely no evidence at this point to support this statement, but I just don't believe the issue we are having is nitrate and or phosphate based. I assume you can have appropriate levels of N03,P04 yet pull out too much bacteria with super aggressive skimming. Worst case scenario is I'm wrong and I can check off one more item that didn't fix the problem and move onto the next.
Keep my posted on what you find, there is bound to be a viable solution to our problem here.
I fully suspect the file fish to be the culprit in
@clhardy5's case.
Regarding
@Edgecrusher28's on going issues its part of a problem that all zoa keepers with larger collections face. I'm not sure what you where targeting with the reef-flux but I've often used chemi-clean as a system-wide treatment when I get something in there bouncing around knocking out zoa colonies. It's efficacy varies greatly. You'd also mentioned testing with a par meter, what was your par in the areas you're keeping zoas? While many strains can adapt to higher par some of the strains that get labeled 'difficult' often times need a lower par that one might run in a standard reef. Hence, we run in the issue of making compromises for one coral or another in a standard reef. One other item that's quantifiable is not so much the alkalinity but the stability of it. In my previous house I had my 125 zoa tank piggy-backed on my 220 which had a lot of large sps and lps sucking alk out of the water. I dosed used a 2 part and came to find out via the trident just how much my alk was varying during the day and causing me issues. This is not something I would have necessarily figured out unless I was testing twice or three times a day on my own. If there's one thing zoas don't like its alk swings - which can be difficult to manage in a mixed reef. I now have a dedicated zoa trough split from the display and don't suffer those issues any more.
You've obviously taken an extremely pragmatic is sussing out all the potential issues and I applaud you for that.
One area touched on but not addressed in your breakdown is feeding. You experimented with running the nitrates higher and lower. How old is the system and do you target feed or broadcast feed? If so, with a Rod's food or Reef Roids like product? Over the last decade I've come to appreciate just how ravenous zoas, especially the larger ones, actually are. In a mature system fish poop and slurry from frozen foods will get the job done for many zoas. However, there's a ceiling there depending on skimming, socks, roller mat and overall nutrient export. Dripping in phyto or the weekly broadcast/targeting feeding of a prepared product has been transformative for me in getting flagging and stalling zoas 'right.'
The other area I'd like to open the conversation to is bacterial and protozan issues. I think far too often we take it for granted that observable pests, pox, nudis, spiders, are the main culprits when in reality I suspect these bacterial and protozan issues are disproportionally responsible for most zoa deaths. This is based on years and years of reading zoa forum posts and my own experience. Post move (spring '21) I've been keeping about 200 strains in my zoa trough (some have been with me 12+ years and through 3 moves/4 systems) and fairly regularly I'd have something come in on a new coral and knock out a few established frags or colonies (or the original host) before I could get it under control. Obviously this is not something that's going to show up on a test but you can tell by observation when something begins to look off. About 6 months ago I started putting every coral that goes in through QT for 9-10 weeks. I've found the results to be dramatic in regards to having zoas melt/pick up an infection. The amount of things I was actively dipping dropped from 10-12 to 5-6 to almost none. It goes without saying that proper husbandry goes a long way. I'm done doing a single Coral Rx dip and then dropping in the frag and hoping for the best. But the question remains, do these bacteria/protozans target specific coral? Or are they like ich where something can come in on a lps and jump to a zoa or sps? I don't know but I'd like to learn more. In the meantime I'm adding a Uv sterilizer based on conversation with other collectors and growers for the times when issues seem to arise out of no where.
In my final thought I'm not claiming to be bacteriologist but I've come to appreciate chemi-clean (as a dip and system wide treatment), cipro, furan-2 (you can still buy the components and make it yourself), and metroplex and how each has a varying ability to resolve issues when zoas just start melting. I've had instances where one did nothing while the other saved the day, and vise versa.
If nothing else I hope this gives you both some additional avenues to consider in figuring out what's ailing your zoas.
