Tank crashed - all fish dead

[bluce]

On my 76 gallon tank - Last night fish were fine swimming around, ate well etc didn’t look to be in any distress. I made a mistake and didn’t turn the return pump back on; checked on them this am, and the water was cloudy and all fish dead. I had a yellow tang for almost 10 years! I’m surprised even with the mistake that all died (Yellow tang, blue tang, flame angel, 3 clowns, and shrimp) - the only things that survived are the rock anemones. The temp only dropped 2.5 degrees, the vortech was still on, so the water was moving, I’ve had the pump go out several times over the years and the fish never died - they have survived longer than 6 hours without return several times. I did a partial water change yesterday and I dosed with no3po4x. I’m thinking it was either the lack of return, or somehow the water was contaminated, or combo of both that did them in? Any thoughts?

 

So now have to decide to wait a bit and slowly restock, or sell off and take a break from the hobby.

[hmoore]

I would bet on something other than the return pump not being turned back on. I lost power in a 135G in Birmingham for 17 hours with zero flow in the tank. Everything (I could see) - including my 2 osc clowns, YT, and Powder Blue - survived. I would occasionally take a jar and lift water and dump it back into the tank to agitate the water. But, I certainly didn’t do that all day since I went to work that day.

 

 

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[hmoore]

And, sorry for your loss bro! But, stay with it. You’ll be glad you did.

 

 

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[zygote2k]

What were the water parameters before the crash?

[bluce]

Haven’t checked in a week or so - tank is very mature, so everything stays pretty stable - until last night i guess.

Last check am 0, nit 0, nitrate 25 (always runs a bit high, but don’t have any lps or spa).

[flooddc]

I doubt not running the return caused fish death. Something got into you water. Get a poly filter and put into the tank to see if any contaminants in your tank. 

Also, check your heater! 

[treesprite]

Did you use any sprays in the room, like air freshener or bug spray?

 

Any children that night have put something in the tank?

 

A curious cat that might have stuck a dirty paw in the water?

[Origami]

My guess is oxygen deprivation due to reduced flow, nightfall, and the no3po4x addition. The additive would have caused a sudden increase in bacteria growth and thus higher oxygen use; corals and other photosynthesizers convert from oxygen producers and become oxygen consumers at night further depleting oxygen; and lack of flow (and separation from your skimmer which I'm guessing is in your sump) reduced oxygen transfer at the surface.

 

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[newbie2014]

Sorry your lose. I guess the lack of the return flow in combination of other unknown factors broke that straw.

 

I guess I should be mindful of my tank too. It's a 40B with five small-medium size fish. I don't have a sump, so no return flow. I stopped using HOB skimmer about a year ago, and I don't use any "bubbler". At night my Vortech is put in Night mode for 8hrs at the lowest speed. When we had that wind storm the other month, we lost power for about six hours at night. The tank temp dropped to 76F, according to Finnex HMX-200 display. No lost, yet. 

[bluce]

Yeah probably oxygen issue plus other things - maybe the no3po4x caused the o2 to get used up without the return. The water I used was a few weeks old, and the lid was propped up 1/4 inch so I could keep a small power head in the container. Maybe something got into the water. I’m just surprised all died at once - wouldn’t you think if it was only an o2 issue that some fish could have stayed close to the surface where the water was being agitated by the vortech mp40? If I do restock I want to make sure this doesn’t happen again...

[Jon Lazar]

With the pump off you lost your return pump and your skimmer. Both are major sources of oxygenation. You also had a fresh dose of NoPox, which is designed to fuel bacterial growth, thereby further reducing oxygen levels. And this is at night, where your whole bioload is consuming oxygen. 

 

Yes, you had a Vortech providing in-tank circulation. That may not have been enough.

 

We lost power when the dericho hit a few years back. Power went out around midnight and I stayed in bed, thinking the fish would surely be fine through the night. In the past, I too had left the pump off before for several hours at a time, while redoing plumbing or some other maintenance. I checked on the tank early in the morning after the storm, maybe 0600 or 0700. Most of the fish were dead.

 

By all means, investigate other possible causes or contributors to your crash. But if you're on a ranch in Arizona and you hear hooves, you should think "horses", not "zebras".

[A.ocellaris]

I would say the combination of NoPox and return pump. When you add Nopox the PH also goes down.