Could it be something in your tank releasing toxins (ie. Sea cucumber, injured fish) I've read on Reef Central about people who were having mystery die off and it was found to be an injured critter releasing low enough lvls of toxins to not affect fish/inverts but could hurt coral.

It's a long shot in the dark and I've looked but I can't find the article on Reef Central to link

If I take out my gfo or let it go too long, I lose sps. Exactly the same as what you describe. And I think I mentioned this before, but testing po4 is next to meaningless. I never get a reading that "explains" it. I just know, no gfo = sps losses.

Maybe ditch the pellets for now. I don't think they're doing anything for you.

What about Ferdinand? Could he be releasing a chemical due to stress of some sort? I know box fish can do that. But I have read about mystery die off being an issue with toxins from a critter as well.

It could also help to ditch the pellets and DI like kein and tony said. I would start from the beginning and bring it back to simple.

I also can't remember...are you running a calcium reactor?

Professional aquarium water testing.

http://aquariumwatertesting.com

This is exactly what I think I need, can you get them locally?

I remember this disaster for people, I thankfully avoided it because I almost never run carbon. I actually haven't been running carbon since this all began, though tonight I put some ROX carbon in a bag in my filter sock in case this is somehow an organic toxin.

This thought keeps crossing my mind. I know they produce more ostracitoxin when they're stressed, but if there ever was a fish that seemed un-stressed it's this guy. The only time he looks stressed is when he's doing his belly-against-the-glass fin wiggle when he's decided it's time for me to feed him. I'd re-home him if I could find a tank he'd do well in, but at 10 inches there aren't many of them around. None of my sessile inverts or my other fish have exhibited anything I'd call symptoms of poisoning or illness though, so I'm having a hard time pinning this on him. I added GAC back to the tank tonight on the off chance this is somehow an organic toxin.

And no, no calcium reactor. I've always dosed a three part mix and switched to the tropic Tropic Marin 3 line after this all went to h*ll in March. I thought I had brought it back to basics when this all started, but without dosing my alk drops to deadly levels in 48 hours, and without pellets my nitrates just keep going up. I'm not sure where they'd stabilize, but it was going to be in the many tens of ppm for sure.

It's death at the growth tips? What do you think causes it? I know GFO adsorbs more than just P. Based on this I put the GFO back online tonight as well as the GAC. I feel like those pellets have me by the balls though. Without them, my nitrates rapidly leave the range acceptable for SPS, but I can never rule them out as a cause for this.

Thank you, I'm going to contact them tomorrow.

I think your spot on with the ALK... A swing from 5.5 to 8.5 is pretty big within a couple of weeks. My tank went from 6-8 and I lost several colonies and almost all growth tips were burnt. I opted to stick with reefers best and reef crystals salt due to the low ALK in the mixture. Fluval is very high in ALK which was my problem.

On a side note, I would do some calculations on how much you should be dosing and measure to ensure it's dosing the right amount. After messing with dosing for a couple of months, I dropped it and picked up a calcium reactor. I would never do an SPS tank without one again.

My alk recently went south and I raised it from about 4 to 8 over a few days, no issues with anything burning. Not sure I'd blame alk.

Gfo also messes with your alkalinity not a huge amount but it drops a bit , Randy has it noted and how much roughly it pulls out, this is a concern to sps guys who keep low alk or carbon dose.



I lost most my sps a while back remember to a alk overdose , the climb from 6-9 dkh resulted in rtn and then I pulled the doser the drop caused me as much harm as the raising did.

The cow fish is a concern too I would think.

Do you make your own food? If so Is it Possible that something changed and maybe contaminated?

Sure does seem like something is leaching (or accumulating) in your water. It was corrected for a while with massive water changes, and then came back. You could try the massive water changes again, to see if again that fixes it, at least for a while.

Meanwhile, would keep testing your water. Not sure if our standard copper water tests are granular enough at the low range, but might be worth doing if you have them.

Alk swings are not good, for sure, but hard to believe it would cause RTN to that extent though, and so suddenly. I have had swings between 7 - 9, but no effects that I could see.

And hope you are past that hydrogen sulphide stuff with your pellet reactor. I definitely don't like the recirculating types. As others have said, would ditch that for a while, too, until you can figure out what is going on. Your higher phosphates are not good either, but again, shouldn't have caused the sudden RTN, I don't think.

Anyway, keep us informed on what you find. We all want to learn from this, if we can.

Ive been watching a tank (established for years) do what your is doing since they added biopellets. all sps are receding. what brand are you using?