How to save the tank ? - The Planted Tank Forum
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post #1 of 11 (permalink) Old 01-11-2018, 11:43 PM Thread Starter
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How to save the tank ?

I left 2 days, came back to a hecatomb in one of my tank. It's a 30L (appr. 10 gal) planted, low tech tank with cherry shrimp and pond snails.
I still don't know what happened, when I came back 5 out of 10 adult shrimps were dead, along with all the babys and a lot of snails also, and the water was cloudy and horribly smelly. I saved the 5 remaining adult shrimps and they are doing ok now in another tank.
Anyway, I did a big water change, but the plants started melting away and now there's a weird brownish/orangy film at the top of the water, it's still extremely cloudy and smells really bad. I changed the water again and it came back... Is there something I can do to save the tank ? I don't mind doing a cycle again, but I'd like to avoid dumping the plants and the gravel+soil if I can help it...

Any ideas ? More water changes until it stops ? Many 100% water changes ? Or do I need to tear down the tank ?
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post #2 of 11 (permalink) Old 01-11-2018, 11:58 PM
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Have you checked ammonia levels?

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post #3 of 11 (permalink) Old 01-11-2018, 11:58 PM
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How long has the tank been set up? I don't know what would have happened in just two days to cause this other than someone doing something to it. Even if a single shrimp died...not a big deal. Tank should be able to handle that. If there were several that died at once...then perhaps you had a big ammonia spike and bacteria bloom. So maybe the 5 dead you found died first and caused the carnage? Who knows.

If the living shrimp are out...I'd do a 100% water change and make sure to clean the filter good. You really should use tank water but in this case...probably better to use something like RO or distilled water. That way it's clean and bacteria loss will be minimized. Vacuum the gravel really well too to make sure that all the dead stuff is removed to prevent more ammonia.

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post #4 of 11 (permalink) Old 01-12-2018, 01:01 AM
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I would remove the plants and put them either in a new aquarium setup or, if just stem plants, in a tub or bucket with a light over it. Be sure to rinse them all very well in tap water first (the little bit of chlorine/chloramine won't harm the plants for such a short time, but might help get rid of any noxious bacteria or other nasty stuff). If the leaves are melting, most stems can recover from solid stem sections (without leaves) if the initial problem is corrected. Plants that grow from a crown (swords, crypts, etc.) can usually recover as long as the crown remains unharmed. Often the leaves on these plants will naturally melt "by design" anyway when environmental parameters change, with the new leaves adapted to the new conditions. Just be sure to remove every bit of decayed tissue and even a bit of nearby living tissue (but not the crown!), just to be sure you got it all. Plant stock can be renewed with as little material as a few nodes of a stem plant and a viable crown with a root base (no actual leaves or roots) for crown-type plants. As for the rest of the setup, not knowing what "soil and gravel" you have, it's hard to say much about it. With basic, inert gravel or sand, it can be washed and sterilized and reused. Soil? Can't really say without knowing what it is. It might could be saved and tried (tentatively) again, but not with anything important (at first, anyway). Wish I could give you an idea of what happened so you could be sure to not repeat the disaster, but I don't have a clue.

Good luck with saving what you can.


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post #5 of 11 (permalink) Old 01-12-2018, 01:03 AM Thread Starter
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The tank had been running since july 2017.
I haven't checked ammonia levels, I don't have a kit for ammonia right now.. I tested for nitrites after removing the surviving shrimps and it showed 0.
Probably the dead pond snails are causing this mess, I removed all the dead (adults) shrimps and vacuumed the gravel but maybe some of the pond snails corpses or baby shrimps were burried while I did it, I don't know. My biggest issue is this weird film at the top, it's really hard to get rid off since when the water level drops it's getting on the plants and when I fill it back up there's still some in there. Maybe I should remove all the plants, rince them and replant and do several 100% water changes ? It's really a big mess.
As I said, I don't care if the tank has to run empty for a month after this, the remaining shrimps are doing good and they can stay in the other tank while this one is cycling again. I'm just not sure if it's possible to save the tank at this point.

When I came back I noticed that a lot of the crypt leaves were melted, could this cause the bacterial bloom ?
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post #6 of 11 (permalink) Old 01-12-2018, 01:05 AM
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Without testing, there are lots of guesses that might be true but very little chance of knowing what's the cause. Some history on the tank will also help to get closer with the guessing. An old tank will react much differently than a newly started one.
Some item which caused a large ammonia spike?
Perhaps a water change before leaving and failed to use a dechlor product?
A temporary power failure which was long enough to kill but restored before you got back?
Many possible causes.
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post #7 of 11 (permalink) Old 01-12-2018, 01:06 AM Thread Starter
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Gravel is black quartz, inert, nothing fancy. As for the soil, it's some "nutritive soil" designed for aquarium use, I have it in my betta tank and never had an issue with it.
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post #8 of 11 (permalink) Old 01-12-2018, 04:48 AM
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Here is one scenario:
anaerobic bacteria built up a "bubble " of H2S gas which eventually "burped" creating a chain reaction event.
h2S kills stuff.. hetrotrophic bacteria multiply pulling O2 out of the water.. more death.. more bacteria..less O2.

you said it smelled bad.. like rotten eggs? H2S

Hydrogen sulfide (sulfate reduction) generally results from the bacterial breakdown of organic matter in the total absence of oxygen, where as de-nitirifcation (nitrate reduction) that lowers nitrates while producing free nitrogen generally happens in an environment that is mostly devoid of oxygen but not completely devoid as in hydrogen sulfide production.

The production of Hydrogen Sulfide in aquariums (both salt and even more so freshwater) is a controversial subject, often with unclear answers as to whether anaerobic de-nitrification is beneficial in freshwater due to the POSSIBLE production of Hydrogen Sulfide.
The keyword is “possible” as in saltwater, you CAN have de-nitrification with no or low hydrogen sulfide production.

With the most current research (although admittedly not conclusive in my view), you CAN have anaerobic de-nitrification and NOT have dangerous levels of Hydrogen Sulfide produced in both fresh & saltwater. With healthy de-nitrification it is possible to have low nitrate levels below 20 ppm
Scum could be iron sulfide which will precipitate out of the H2S enriched water..(conjecture)
Bogs have a tendency to have this type of scum at their edges though a different iron compound..
Maybe a later oxidation to Fe Hydroxide (haven't chased the chem down )
With a lot of organic waste left in the water and soil it will not "clear" for some time due to bacteria populations continually increasing..
even w/ water changes..

IF the above seems plausible you will need to replace or fluff the soil to remove gas and add O2..
Hydrogen Sulfide in Aquariums

rotten egg smell is pretty diagnostic...........

. But if the oxygen is low, or the amount of H2S high, it is lethal to everything in the tank.

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Last edited by jeffkrol; 01-12-2018 at 05:11 AM. Reason: edit
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post #9 of 11 (permalink) Old 01-12-2018, 09:01 AM Thread Starter
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Looks like you're right... I had no idea this stuff could happen... I didn't vaccum the gravel for quite some time before that because I was afraid of sucking up all the new born shrimps... Only water changes through an hose blocked with aquarium polyfill... It smells like rotten eggs and the stuff is of a rusty color.
Man what a mistake... So now, what should I do ? "fluff up" the gravel with a fork or something and several 100% water changes until this is cleared ? Or remove all the water, rince the plants, remove a good portion of the gravel and rince it in water+small amount of bleach to kill all bacterias or something ?

How should I vacuum the gravel when baby shrimps are all over the place in your opinion ? For the future
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post #10 of 11 (permalink) Old 01-12-2018, 10:20 AM
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You can syphon into a bucket and catch out any babies afterwards. Disturbing the gravel even if not syphoning helps e.g. poke it with a stick regularly. If you have any deep areas that aren't planted reducing the amount of gravel will help too.
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post #11 of 11 (permalink) Old 01-18-2018, 03:27 AM
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Yep, the "rotten eggs" smell pretty much nails it. Many decades ago, before the rise (and fall) of the undergravel filter, they called it "sudden tank death syndrome", so it was common enough to be labeled. That was before the gravel vac' as well, and to prevent it, they would stir the substrate with their finger while syphoning mulm from the aquarium. With the introduction of the undergravel filter, water circulated through the substrate, preventing pockets of the anaerobic bacteria that produces the toxic Hydrogen sulfide gas. Now that the undergravel filter is no longer the first accessory recommended for an aquarium, we've come full circle and the issue once more becomes a problem. In a planted tank, the plants circulate enough oxygen into the substrate from their roots to prevent major pockets of anaerobic activity (and thus toxic gases), but areas without such root activity are still subject to the problem. Most of the time, the issue never arises because, although most aquarists no longer use an undergravel filter, nearly everyone uses a gravel vac', so any anaerobic pockets are usually disturbed before toxic gases build up to a dangerous level. The problem arises now because it is not common enough that everyone is aware of it, so when there seems to be a reason to not vacuum the gravel in the usual way (as in your case of not wanting to suck up baby shrimp), the anaerobic condition is allowed to go undisturbed and gases build to the point that they bubble up, "killing" the tank.

I guess it's really a case of "those who do not know history are doomed to repeat it", huh? I know about it from my mom's old aquarium literature, yet it's so rare now that it didn't even occur to me (nice call, jeffkrol!).

But as for removing a film from the water's surface (without a surface skimmer), you can gently lay a paper towel on the surface, then pick it up from the center. The scum or film is trapped by the paper towel and you just toss it. You may have to do this a few times, depending on the size of the aquarium or the amount of film.


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