I've got three opinions for you. My first step is the most important as it rules out MANY little critters and all pests. It may be a mix of a few things though. Each of these suggestions is it's own little recipe to solve each problem.
1) The first thing to do immediately, go to any petshop and get Melafix -- Any version works but I suggest POND, as it's stronger.
Dip your corals in Melafix, and if you go through with this ask me all about it. There's a bit of information to using Melafix and I will walk you through the process. I suggest this dip above all, if you have any pests (even very unusual ones) this will kill them. From any type of worm, to SPS spiders, to nudis, to pyramid snails. It will kill anything.
But seriously ask me about how to use it, as it depends which version you get.
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2) This is what I would look into immediately. You don't want zero po4, I would suggest an absolute minimum of 0.05, ideally more like 0.10+. It's a myth that SPS dislike phosphates. And cutting phosphates to zero is basically how you speed-kill corals, especially zoas in my experience. Yes, I saw you fed more and that it didn't help, but feeding isnt exactly the same as a controlled dose.
That's where my bet would be first and foremost. I would pickup Seachem Phosphorus and dose that.
I would also suggest the follow taboo's
- No filter socks
- No chaeto
or dose Chaeto supplements
- Dose po4 to 0.10
- Get no3 to 20-25
If this does not help, I would then assume it's likely that you're greatly undervaluing the rust issues on your return pump. Lastly it's possible you have an unusual pest (Bobbit worms eat corals when young, and are too small to eat fish, for example).
On Rust: Tunze is the only pump where some magnet rust is okay, because they use a different magnet that makes an inert form of rust that doesn't harm our reefs. They do this at great cost to them, because that's how you make the best equipment on the planet. Yes, I'm slightly biased when there's good reason to be!
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3) So the first thing I would say, is that 0 water change systems with Fuge that are NOT dosing essential elements becomes a problem over time.
How this problem manifests in order (lacking trace)
- Macro uses all trace
- Macro stops taking up nutrients
- Corals SLOWLY begin to pale (can take months)
- Corals slowly begin to STN
So if you are using ATI essentials, or Triton system, or just dosing something for your chaeto (it strips the water of essential metals) then you're fine. If not, this probably isn't the problem, but it isn't helping and may just be another straw on the camels back.
My symptoms were exactly what you're describing. You'd think i'd put this first in that case, but it's all good info to weed through.
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4) Stability issues
- Salinity
- Temp swings
- Alk swings
- High alk + Low nutrients?
- High Lighting + Low nutrients?
- High Lighting + High Alk + Low nutrients?
- Cal/Mag
- Wife randomly spraying the room full of fabreeze daily?
