Even sadder day

[OrionN]

.... At night my oxygen was falling below saturation. During the day photosynthesis brought it above saturation. I think some on my fish die to lack of oxygen! ......

Jim,
I am sorry to hear about your problem. I think you are right on here. Death of fish with corals not affected and recnet loss of surface skimming suggest O2 problem. Good luck with your problem. you must be broken-hearted with the death of your fishes especially the angels.
Good luck. I use a PM bullet XL2. I love it.
Minh

[GaryP]

I had a similar problem with my first tank. In this case it was because of hair algae dropping the oxygen level at night. O2 saturation in saltwater is only about 7 ppm, as opposed to about 13-14 ppm in FW. Fish start to crash at anything less about 5 ppm. That's a pretty narrow window. It would make sense that fish die-off would occur at night when there is no oxygen being produced by the algae in the tank.

Gary

[Instar]

I have several observations on this:
First, the pH is not low enough to indicate a condition of extreme O2 depletion, CO2 build up.
Second, the only way to crash the oxygen saturation is to stop running the over flow into a sump or part of the sump or a makeshift sump while working on getting a new refugium. Did you do that? A good over flow and spillway like it should be done, should be vortexing the water enough to compensate for a lot of the CO2 build up at night. Since CO2 is heavier, it can also go over the overflow and to the floor, thereby creating a clear zone for surface agitation at night in the main tank.
Next, what is the measure of the ALKALINITY? Meq/L or dKh ??? With that calcium, dkh, pH and Mg, it looks like you have a major shift in the buffer system to a secondary Mg buffer and that you are very out of balance. The corals care less about all this than you can imagine, but, its very hard on the kindneys of the fish. In an extreme, Uremic blood poisoning is then quite possible in the fish. I'd have to see the tank, but, its really not that easy to keep things in balance once you start adding kalk and buffers.
Next, when you fragged that Kenya tree, it was done inside the tank. You need to be running Activated Carbon to remove that toxin created there as well as to remove the Chelators in the I/O (or almost every other brand too) new salt mix. Since you do not have a deep sand bed, mass macro algae beds or deep rock substrate in there, O2 depletion is not as likely to happen at night from microbiol activity. It may go down, but, depletion is another thing.
I am assuming that you are still running an over flow into something. If not, with all that coral in there feeding at night, oh man, you gotta have an overflow going to a sump.
Don't go wild with water changes since it looks like the buffer system is messed up. A little at a time, a couple times a day to equal not more than 10% per day! Do 10% per day for 10 days and then see where you are. The corals may go shocky on you. Run the carbon and don't sweat it. They'll close up till all is stable again.
Hope something here is helpful.

[Jimnorris]

Good news now is all well! Larry somewhere in your respond I think you hit on it (the problem) It took me afew days to hook up another overflow and start skimmimg the water surface.
Thanks all for caring!
Jim

[beareef19]

I hope everthing will get back to normal, aloss like that is some times hard to deal with :cry:

[Instar]

Jim, I am really sorry for all that mess. I don't believe it was the O2/CO2 and lack of an overflow alone that did the fish in though. Those wrasses and blennies shut down thier respirations at night and the demand for O2 is very low with them. They, and the angels do have something in common though, that separates them from the tangs. The tangs are obligate herbivores and the others are omnivors. Their metabolism of protien is different. O2 saturation went down the first night, yet all the fish survived. Since all of the ones that passed metabolized protein to a greater extend, they would have a higher urea and creatin production than the tangs. With the dKh so elevated as to keep the pH above 8.2 without the overflow, and depress the Calcium to 425, the balance is a bit off. In that lies the reason I said blood poisoning because kidney function is related to the buffer-acid-base balance and the tangs don't have as much of that to get rid of. Blood poisoning takes longer to show up. I thought you had a calcium reactor; don't you? The sump and refugium is only part of the picture, I think. I hate to loose even a small thing let alone all you lost. Ugh! A domino effect of things. If you need help, I'd try to be useful if I could.