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Discussion Starter · #1 · (Edited)
I didn't really know what to title this thread, this is more of a post trauma question, as everything is fine now but have no idea what happened last night. My google searches have been rather fruitless.

50 gallon tank, well established low tech, with lots of large anubias, Fissidens fontanus, and various crypts. I had everything pretty perfect for the past 4 years, 20% water changes monthly, bi annual filter cleanout, light cycle, etc.... I haven't lost a single fish in 3 years, but my crypts have been slowly dying off as i haven't changed the substrate in over 4 years, and due to life stresses not to do with my tank i had a large BBA infection sneak up on me.

Saturday morning I finally decided to spend a couple hours and get everything fixed up again. Pulled everything out of the tank (plants, rocks, wood etc) Brought the water level in the tank down to 25% (fish still in it) and delicately removed about half of the old florite and replaced it with new. Sprayed wood, Fissidens fontanus, anubias, and rocks with hydrogen peroxide (50% Hp, 50% water) solution to kill off the BBA, trimmed roots on all plants, re-planted and re installed all plants wood, rocks etc.... Then refilled the tank with (50%ish new water 50% old water) I used proper de-clorination, and dosed with my regular dosing of phosphates, minerals, etc...

Skip ahead to last night (36ish hours later). Prior to the lights going off all the fish were happy as clams, BBA was turning a satisfying magenta color, water was nice and clear, things looked just fine. I am then awoken at around 2:00 am (6 hours after lights out) to a thrashing noise, and turn on the lights to see the worst cloudy murk i have ever witnessed in any of my tanks. My angels are dead, all my schooling fish (various rasboras and minnows) are dead or gulping for air desperately at the surface, and my cory's and otto's are rushing to the surface and almost jumping out every few minutes. I added an air stone and checked Amonia, Nitrate, nitrite, and all are 0 or below .25. After frantic google searching I lowered the water level to get additional surface agitation, turned the light on hoping the plants will help in the process, pulled the dead bodies out :( and went back to bed.

I woke up at 7 this morning (5 hours later) the tank is mostly clear, cory's, otto's, and one very sad looking lamp eye are all acting like nothing ever happened. Re-checked the water and everything is still below 20ppm.

I think the crisis is over but I really want to know what the hell happened so I don't do it again? I found it particularly strange that all the bottom feeders and cleaner fish survived and my "robust" fish like White cloud minnows died off. I really would have expected my Otto's to see the toilet first!


TLDR: Established tank, 50% water change, 50% substrate replaced and BBA nuke, fine for 2 days, turn on lights, fish dead, tank cloudy, 5 hours later like nothing happened.
 

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I am not sure of an answer. I do have a question though. Why did you replace the fluorite with new fluorite. I am pretty sure that stuff last for years and years. Next time I wouldn't bother.
 

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Discussion Starter · #3 ·
I am not sure of an answer. I do have a question though. Why did you replace the fluorite with new fluorite. I am pretty sure that stuff last for years and years. Next time I wouldn't bother.
Yep, I agree but the old florite was pushing over 4 years old, and my Crypts were shadows of what they once were. I thought about using fertilizer disks in the substrate but have had mixed results with that in the past.
 

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I have a tank that has had the same Flourite in it for at least 15 years. My crypts would take over the tank if I didn't constantly pull them up.

I'm kinda sorry I even planted them. They look nice, but they grow too darned fast.

Anyways, as for what happened with your tank...what were your test readings? There's a big difference between 0 and "less than 20."

Though it sounds to me like the problem was lack of oxygen. Perhaps due to the dying algae? The bacteria that eat dead plants absorb oxygen. With no plants producing it at night, it might have been too much for your tank.

I have noticed that products sold for killing algae usually recommend that you increase aeration/lower the water level in order to avoid this problem.
 

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My first guess would be a large bacterial bloom.. Probably caused by killing off a bunch of de-nitryfying bacteria due to the massive change out.
Bacteria may have sucked all the oxygen out of the water
Then again you didn't mention if the pH shifted.. which I also would suspect..

sorry only guesses..
Major causes of rapid cloudiness and rapid decrease in cloudiness would be precipitates or bacteria..
Precipitates would normally be immediate. Bactera could take some time
 
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Discussion Starter · #6 ·
I have a tank that has had the same Flourite in it for at least 15 years. My crypts would take over the tank if I didn't constantly pull them up.
Huh, Maybe i made the wrong assumption as to why they have been stunted growth wise. I assumed it was lake of root nutrients as my anubias are still growing happily.


Though it sounds to me like the problem was lack of oxygen. Perhaps due to the dying algae? The bacteria that eat dead plants absorb oxygen. With no plants producing it at night, it might have been too much for your tank.
This makes sense, but i have never experienced something this crazy fast though. Maybe it was a combo of the organic material being stirred up from the substrate and the decomposing BBA? This makes a lot of sense.

Bump:
My first guess would be a large bacterial bloom.. Probably caused by killing off a bunch of de-nitryfying bacteria due to the massive change out.
Bacteria may have sucked all the oxygen out of the water
Then again you didn't mention if the pH shifted.. which I also would suspect..

sorry only guesses..
Major causes of rapid cloudiness and rapid decrease in cloudiness would be precipitates or bacteria..
Precipitates would normally be immediate. Bactera could take some time
I didn't even check PH DOH! Ill do that when i get home. I am leaning toward bacteria sense the cloudiness didn't show up the for almost two days. I agree with the bacteria sucking oxygen out.

Bump:
Anyways, as for what happened with your tank...what were your test readings? There's a big difference between 0 and "less than 20."
Missed this one. It was the ammonia, and its hard to tell in that range between colors for me with my liquid testing set. I didn't give the right units either It was somewhere between the .25 and the 0 on the low end of the scale.
 

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Discussion Starter · #8 ·
"old tanks" generally have a pretty low ph. If your tap was quite high in pH you had a massive pH shift..
Percent toxic ammonia increases w/ pH btw..
% Of Toxic Ammonia Charts - Tropical Chit Chat - Tropical Fish Forums
The only reason why I don't think this is the case is the Otto's survived like nothing happened and I thought they were like canaries in a coal mine with PH. I would have assumed a PH spike would have been immediate, rather than 2 days later.
 

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Well my point was a pH spike (not the only possible cause btw) knocked out a bunch of bacteria. May have even been short lived..but enough to release a large consumable bio-load..
Chain reaction type situation..
Reason I lean to this is something similar happened w/ my switch to pressurized CO2. After my initial futz w/ delivery systems and levels I experienced a large bacterial bloom.
It did last more than 1 day though. Like 3.
My best guess was that I killed off almost all my canister bacteria which got flushed into the tank. Then consumed..

Didn't lose any fish but the tank probably stayed more "stable" than the canister that probably sucked in some large bubbles of CO2 which just shifted the "local" environment..
Tank itself was heavily planted and high light...so may had a chance to "sop" up the CO2

Unfortunately this is an opposite scenario to what you may have had.. Going from acid to alkaline where mine may have went from alk to acidic..
Then again that would have cut down on the ammonia toxicity level where yours would have went the other way..

removing 1/2 of the bacterial stuffed fluorite probably didn't help either..

Whatever the cause, massive shifts of a "well established" tank are never recommended..

http://www.aquariumcarebasics.com/aquarium-water-quality/cloudy-aquarium-water/

A bacterial bloom consumes large amounts of oxygen from aquarium water, so from the onset of a bacterial bloom make sure the tank gets additional aeration. Also, a bacterial bloom may coincide with rising Ammonia levels, so be sure to routinely check for Ammonia spikes.

Damaging or destroying an aquarium’s biological filter may cause a mini-cycle or a full blown aquarium cycle…further complicating matters.

Pretty sure it fits in those categories somewhere..
FUN Facts on bacteria:
Nitrifying bacteria reproduce by binary division. Under optimal conditions, Nitrosomonas may double every 7 hours and Nitrobacter every 13 hours. More realistically, they will double every 15-20 hours. This is an extremely long time considering that heterotrophic bacteria can double in as short a time as 20 minutes. In the time that it takes a single Nitrosomonas cell to double in population, a single E. Coli bacterium would have produced a population exceeding 35 trillion cells.

None of the Nitrobacteraceae are able to form spores. They have a complex cytomembrane (cell wall) that is surrounded by a slime matrix. All species have limited tolerance ranges and are individually sensitive to pH, dissolved oxygen levels, salt, temperature, and inhibitory chemicals.
http://www.bioconlabs.com/nitribactfacts.html
http://www.thekrib.com/Chemistry/ammonia-toxicity.html
 

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Bacteria blooms don't go away in 5 hours. Don't have a cat do you?
 

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I want to start a dirted tank in my 20 gallon tank. It's been established for 6 months doing great! Problem is I'm a college student and I'll be moving soon. Only 1hr ride from my house. Would a dirted tank do well? During a car ride? I don't want to start a dirted tank if it is going to be a hassle to move and destroy my tank. Thanks!
 

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Discussion Starter · #12 ·
Bacteria blooms don't go away in 5 hours. Don't have a cat do you?
I do have a cat. I am missing the connection here.

Bump:
I want to start a dirted tank in my 20 gallon tank. It's been established for 6 months doing great! Problem is I'm a college student and I'll be moving soon. Only 1hr ride from my house. Would a dirted tank do well? During a car ride? I don't want to start a dirted tank if it is going to be a hassle to move and destroy my tank. Thanks!
I have moved this tank twice in the past 5 years. Empty out to almost empty, put the fish in baggies, save your water in jugs. Move to new location, Delicately re-fill using original water, add fish back in. Bit of a pain in the ass but It worked just fine.
 

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I do have a cat. I am missing the connection here.

Bump:

I have moved this tank twice in the past 5 years. Empty out to almost empty, put the fish in baggies, save your water in jugs. Move to new location, Delicately re-fill using original water, add fish back in. Bit of a pain in the ass but It worked just fine.
Cats can attack fish and swat at them in the water until they die of exhaustion. They can't reach the bottom feeders so they wouldn't die. The thrashing around causes gunk to get kicked up killing off any fish weak from exhaustion. Cat gets tired/bored and leaves tank goes back to normal like nothing ever happened.

If it wasn't the cat then it was probably a combination of doing too much. Going from very infrequent 20% water changes to a massive 75% water change, changing substrate that had 4 years of detris built up in it, dosing large amounts of hydrogen peroxide, large change in biomass, presumably cleaning the filter as well. You shocked a well established system and threw it massively out of balance unfortunately. I agree with what other people said, you probably killed off too much stuff and all the kicked up detris caused a massive bacteria bloom, combined with dying algae and less bio mass to produce oxygen during the day your fish probably ran out of oxygen. I doubt it was any one thing (unless it was the cat) but a combination of everything you did adding together.
 

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Bacteria blooms don't go away in 5 hours.
They don't, but he added an airstone, lowered the water level to increase surface agitation, and turned the lights on so the plants would produce oxygen instead of consuming it.

That might have been enough to offset the anoxic conditions caused by a bacterial bloom.
 

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Discussion Starter · #15 ·
Update:

Rechecked all levels and everything is at zero. Tank is crystal clear, and all (remaining) fish are happy.
Looks like i just learned a lesson of don't do too much to your tank at once.

Bump:
Cats can attack fish and swat at them in the water until they die of exhaustion. They can't reach the bottom feeders so they wouldn't die. The thrashing around causes gunk to get kicked up killing off any fish weak from exhaustion. Cat gets tired/bored and leaves tank goes back to normal like nothing ever happened.

If it wasn't the cat then it was probably a combination of doing too much. Going from very infrequent 20% water changes to a massive 75% water change, changing substrate that had 4 years of detris built up in it, dosing large amounts of hydrogen peroxide, large change in biomass, presumably cleaning the filter as well. You shocked a well established system and threw it massively out of balance unfortunately. I agree with what other people said, you probably killed off too much stuff and all the kicked up detris caused a massive bacteria bloom, combined with dying algae and less bio mass to produce oxygen during the day your fish probably ran out of oxygen. I doubt it was any one thing (unless it was the cat) but a combination of everything you did adding together.
My cat has never bothered the fish, so that one is out. I agree with your other thoughts though. I did not clean the filter (thank goodness) as I figured that would be too much. Looks like I did too much anyways.
 
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