Post-water change stress? Several fish hyperventilating...

I did a water change last night in my monster tank and did much more gravel cleaning than usual. Really got it good in one of those quarterly extra deep cleans. Removed a few plants and shifted a couple of rocks too, but it was hardly a full re-aquascaping. As usual, it took a while to settle and make the water clear again but it looked great.

So today I came out and everything seemed great - the Green Terror wasn't beating anyone up and the big distichoduses (which previously didn't like each other) were getting along. But I noticed that the smaller distichodus and a few other fish seemed to be hyperventilating. Their behavior hasn't changed but they're definitely looking stressed out, mouths opened more than usual, "breathing" at a much more rapid pace. It is now night and they're still doing it.

Water parameters are fine - the tap water here is pretty hard, but it's no different than it was before - and I definitely remembered to re-dose my dechlorinator and aquarium salt after the 50% change. Water temp is the same, nothing about the lighting or filtration changed, no new tankmates, etc. So I'm wondering if something else could be wrong. Is it possible that someone is brutalizing them at night when I don't see it? The GT is a real jerk, but usually he's not shy about beating others up during daylight, and I've never seen anyone go near the giant danios, who keep to themselves up top. Plus if there was bullying I'd expect to see some damage to fins/scales.

What's weird is that they're behaving normally and haven't colored down or gotten pale or anything. But it's been all day and they haven't calmed down so I have to assume something's up. I just don't know what. For now I'm of the opinion that I should just give them till tomorrow to calm down, maybe it's just a bit of stress from the water change, but I want to be prepared with some ideas if they're still like this tomorrow.

Well, two hours later, both my distichodus sexfaciatas were dead.

I checked on them before going to bed and things seemed OK. I spent some time on the computer and then about half an hour trying unsuccessfully to sleep. At about 2 I heard a noise out in the kitchen. Sounded like either the cat knocked something off the counter (her favorite hobby) or a fish jumping up and knocking one of the lights on top. Since I just cleaned off the counters, I went out to check. Now, I knew that it would've taken a much louder noise for a fish to have actually gotten out, but since I had some harmony issues recently I wanted to make sure there wasn't a death match going on.

Instead, the 6" was belly up on the bottom and the 9" was nose down on the side. The smaller one had this wide eyed, wide mouthed look of pain on his face. I almost burst out crying. Every other fish was in rough shape too, including a pictus cat on his side. The big lussoso was listless but alive, and the dats were up at the surface looking awful. I immediately started netting them out, starting with the dats, and put them into my 55g planted tank. It's already pretty heavily stocked, and there are some tetras that could become snacks for the AT, but I had no other options. My hospital tank is already in use for a jurupari with severe septicemia.

The green terror and convict were saved for last, and since they're really mean I sprinted down the hall to the bedroom and dumped them into my 55g mbuna tank. The pH is higher but I've had some small fish handle the change without issue and I figured that can't be any more stressful than what they were already going through. I also put my ghost knife, the giant syno cat (he grew up in that tank), and two other large-ish silver shark cats there, since they'd just destroy the planted tank and are even more likely to eat tetras than the datnoid.

As devastated as I was by the loss of two of my favorite fish (who are impossible to replace) I am equally glad that I decided to go check on a noise I would have ordinarily ignored. There was no way the other fish were going to make it to morning. I'm happy to report that they all seem to be OK in the other tanks (knock on wood), although the planted tank inhabitants aren't all that thrilled.

So... what could possibly have gone wrong? I'm a veteran fishkeeper so I couldn't possibly have done something ridiculously stupid, could I?

My best guess is, well, sort of, yeah.

A week ago the planted tank was looking a bit unclean for my tastes. The other two tanks are crystal clear at all times but that one has little particles constantly floating around. Between that and the fact that I had recently trimmed out about half the tank, I wanted more filtration on it. I had previously removed an Emperor 400 from there to do backup filtration on the big tank, since the dats and distichoduses were messier than I anticipated. In anticipation of receiving my FX5, though, I figured it'd be OK to move it back to the planted tank. So on thursday I did, leaving only the Eheim canister on the big tank.

So lately my powerhead has been losing suction and falling off the glass. I put it back whenever I notice it but it just falls back off again. It had fallen off before I went to bed and I didn't fix it. This is no big deal though because it's over a foot below the surface anyway.

What I never noticed, however, was that across the tank, on the side, the Eheim's spraybar had also lost suction. Normally it sits about an inch below the surface; when the water level evaporates down to it, that's usually when I do water changes. When it undid itself it slipped about another inch down.

If this had been my mbuna tank, that'd be no big deal, because I have those spraybars angled up, to guarantee adequate surface distortion. Since I had a HOB on this tank, though, there was no need. So they angled straight out.

So basically, my best guess is that I knocked it off at some point saturday night during the water change and never noticed that I wasn't getting any oxygen exchange. For an entire 27 hours.

I'll be taking a sample to the LFS to see if they can do any tests beyond the standard stuff I can do, but I'm pretty sure that I inadvertently killed two of my favorite fish.

Mods, since I'm 80% sure this was what happened, this thread might make a good entry into the "Lessons learned" forum.

DAMN IT.

It occurred to me that there was still some oxygen exchange, though minimal, because when I fed them this evening I could still see some ripples. So they were stressed, but not about to die.

And then I dosed a whole lot of Melafix. Right before I went to bed. And killed them. It was basically like putting a bag over someone's head.

I hate myself.

Thanks.

I'm so upset I haven't been able to sleep at all. I just keep thinking of that feeling I had when I walked into the kitchen and saw them like that. My initial thought was that the whole tank had died. I guess I'm pretty proud that I stayed level-headed, noticed the dats gasping, and acted quickly to get everyone out. So far, knock wood, everyone is OK and the lussoso has recovered.

It's not all good news though. Unfortunately I think the jurupari (in the hospital tank) is a goner. He was my first big fish purchase 18 months ago, followed shortly by the smaller distichodus, and now I'm going to lose them both in the same day or two.

(on a slightly happier note, my green terror looks AMAZING in my mbuna tank, mixed in with demasoni and labs and under the lighting I've got set up for them... his colors are so vibrant, and this is after being there for just a few hours, in PH .7 higher and water that's way too hard for his natural tastes. He looks so good I'm tempted to leave him there, even though it defies all logic.)

Live and learn, I guess. I now know just how important gas exchange really is, and also that distichoduses are far more sensitive to it than other fish (and south american cichlids seemingly far less so - they were the only fish that were even remotely tough to catch). It just really really sucks that it had to be those two fish. The little guy had one of the best personalities in any of my tanks and the big one had just started to come out of his shyness and become social. And they're just such cool, bright fish.

That was my first thought. But if it was that then all my tanks would've been screwed, since I did water changes on all 6 of them and used the same 1 drop/1 gallon of the dechlor that I always use.

The Lussoso is doing well and I put the AT back in there too with him since I think he ate two tetras. Both seem happy. So I'm 99% sure it was just the O2 issue. I'm taking the water in to a few fish places today though to see if any can test for other stuff like chloramine, copper, pollutants, etc. And a backup check for ammonia just because the only test kit I could find for that could be 10 years old and not work. Been a while since I was at all concerned with that but you never know.