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What killed all my fish (but none of my shrimps) after moving them to new tank?


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Posted (edited)

(Warning: Pictures of dead fish)

Hello. A few weeks ago, I moved. My wish were in holding tubs with their existing filter etc, and were doing fine. Four days ago, I scaped their tank again, after I cleaned it with water and an algae scrubber only. I also bought some new decor (the large piece of wood, the larger green rocks and the smaller light rocks/pebbles) in addition to their old decor. Their old decor (the other rocks) were sealed in plastic bags while still wet for a week or so after I moved (first I thought maybe I want to keep some of the living organisms on it alive for my hillstream loaches and add them instantly to their holding tub, but I did not do that). Then for three or four days, there were able to dry in the scaped but not yet filled with water aquarium. In the back of the tank, I also added some of their old sand back, which was also sealed in a container in its wet state for a week or so. But I did wash this sand 4-5 times with fresh water before putting it in the tank.

Yesterday, I filled the tank with water once, shuffled the sand around a bit to release air bubbles, drained it again mostly, then filled it up completely with maybe 5-10% of the water coming from their old holding tub. I added some additional beneficial bacteria from a bottle as well as some Catappa leave extract. I added the filter, as well as a bag with small lava rock that was also in the old aquarium and in the holding tub. I added the plants, 5 amano shrimp, my 4 large and maybe 15 baby/young hillstream loaches, around 20 male endlers and lots of neocaridina. I also added one (I think its called) black devil snail from my other aquarium/holding tub. All fish from the other tank, which I also added all the fish to yesterday, are fine.

All fish are dead. I added them maybe 13 hours ago. I last checked in on them 8 hours ago. then I went to sleep. In retrospective, a few endlers were "laying down" on the gravel (not upside down), but I sometimes observed this in the past, which was mostly hiding from their peers to take a break. Maybe the largest sign I missed was that the hillstream loaches were very much only sticking to the glass of the aquarium and did not really go on their new rock pile.

The shrimp are doing fine, I'm not sure about the snail right now, it might also be dead.
Obviously I will tear down the whole tank. I will also not replace it with anything and just keep the other tank for now. But I don't know what to do with all the decor etc. now - I don't want any of it to kill my fish in the future.

- Maybe the wood leached something in the water? I did not water it beforehand.
- The large green rocks had some what looked similar to package tape around them when I bought them. I previously had fear around this kind of glue residue on rocks, also from bar code labels that were put directly on rocks, but never had any problem before, so I did not scrub the rocks beforehand. I figured they woudn't wrap aquarium rocks in stuff toxic to fish..
- Maybe some deadly bacteria build up on the old rocks or sand? I would have thought the drying process for the rocks and rinsing for the sand would be enough
- There was no visible nitrate/nitrite yesterday and also not right now. Maybe still an ammonia spike? I did feed a little bit yesterday

It must be something that shrimp are not affected by... I am so sad right now, this was my absolute favorite aquarium of all time and I wanted to make it even more beautiful for my fish in the new apartment 😔






Edited by Max
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Posted (edited)

So sorry to hear. Sadly, these sorts of things happen to almost every aquarist who has remained in the hobby long enough.

It can be very difficult to diagnose the cause of your fish death. I will provide several possibilities. It may be due to something else entirely.


For beneficial bacteria colonies from your previous set-up to remain alive and healthy, they need sufficient oxygen. One possible cause of your loss is that the aerobic  bacteria died off, leading to an ammonia spike. Fish release ammonia from gills via respiration. Their waste also releases some. But if there is an insufficient beneficial bacterial colony established, ammonia will become lethal. When you add a liquid bacteria, you are actually seeding the tank with bacteria that is in a cystic-like suspension. It takes some time for that colony to begin activating. I've heard some people say, "Just add Fritz-Zyme 7 [or Dr. Tim's, etc.] and add fish right away!" This assumes a number of things: (1) There is not already an ammonia-releasing buildup in the water; (2) The Ammonia release rate of the new fish will not outpace the bacteria colony multiplication rate needed to convert ammonia to nitrite and nitrite to nitrate; (3) Additionally, it assumes that there is sufficient oxygenation of the water to build up healthy bacteria colonies.


That third issue, insufficient oxygenation, is another possible cause of your fish die off. If your autotrophic bacteria colonies were not healthy or large enough to dial in your ammonia spike, typically a bacterial cloud builds up in the water. This is due to heterotrophic bacteria -- the "cloudy water" commonly seen in some newly setup or newly reset aquariums. Heterotrophic bacteria in and of itself is not usually a problem. However, heterotrophic bacteria consumes a _lot_ of oxygen. I have lost many fish due to insufficient oxygen. As Cory frequently says, "add an air-stone." This keeps oxygen flowing into the aquarium, allowing autotrophic bacteria (the good colonies that you need) to catch up. The cloudy water will eventually disappear. Another important step is adding an ammonia-binding chemical such as PRIME or AMQUEL that will lock up ammonia spikes over the short run.


Adding wood and botanicals may draw down your pH significantly. Other chemical reactions are settling out in any new tank as well. Unless you're prepared to carefully comb through and test parameters: pH, NH3, NO2-, NO3-, KH, GH . . . perhaps even TDS and DO . . . you're gambling with any new tank setup or any tank reset. In my opinion, the safest way to manage this is to give the aquarium several weeks to settle, adding beneficial bacteria and oxygen. Test carefully and be sure you know your parameters before adding your fish.

Now, I was able to shortcut that wait recently. Here's how...

(1) I bought a 45 gal. from a friend. I asked him to leave the substrate in.

(2) I added water and set up a canister filter, and then squeezed in a HUGE sponge full of beneficial bacteria. Here is what it looked like...


After a day, it had begun to clear. All of that live bacteria was building up in the canister and in the substrate.


I waited until the water was completely clear. Then added a fully seeded sponge filter, a venturi with pump drawn though another sponge filter, then rocks and java moss from the old tank. My aim: lots of beneficial bacteria!


Only after this, I transferred the fish. But because the aquarium was already established, they all did well. 


Here are several videos of the aquarium up and running. I did not have to wait weeks. Just added very healthy bacteria, loads of oxygen, and tested parameters. These are native US Fish, not tropical...


Now, the fish are spawning in here already...


Edited by Fish Folk
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I’m so sorry for your loss. I agree with @Fish Folk on everything. 
I just want to add that some apartment complexes use massive water softeners and other filters that strip the water and some do not. There may have been a major water chemistry change from the tap. 

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Thank you. I'm from Germany and haven't heard about the use of water softeners. I only moved a few kilometers and the tap water seems to be similar. The second aquarium is still doing fine, so for now I think it does not relate directly to my tap water. What I did see today when comparing my test strips from both aquariums is that the one where all my fish died had a lot higher kH. I assume some of the new rocks I bought are raising kH, even though the people at the store said they would not... So maybe this was enough of a chemistry change to kill the bacteria?

I do think something had to kill the bacteria, because I added the whole sponge filter, additional established lava rock media and then in addition the liquid bacteria. From what I was told, the liquid bacteria I usually buy is active faster, because it is refrigirated. But this was more of a backup, I expected the established bacteria to be enough, because it always was in the past. This is the very first time I had this issue, this is probably my 10th+ setup of an aquarium. Most of the time I use some filter media from an established tank, but usually I do add fish/biological load way more slowly. But for example, the move from the aquariums into the holding tubs went without problems, I basically moved everything except substrate and hardscape to the tubs. I often hear fish youtubers talk about "its just like a 100% water change" when doing something like this (though in the case of moving the fish, I also moved like 50% of the water to be extra safe). I did reduce feeding by like 90% while they where in their holding tubs.


That third issue, insufficient oxygenation, is another possible cause of your fish die off. If your autotrophic bacteria colonies were not healthy or large enough to dial in your ammonia spike, typically a bacterial cloud builds up in the water. This is due to heterotrophic bacteria -- the "cloudy water" commonly seen in some newly setup or newly reset aquariums.

This might actually be it, because the water is indeed cloudy (especially compared to the other tank, which went to a basically identical process but is very clear) What I don't understand is where this heterotrophic bacteria comes from - is this part of the liquid bacteria? Or does this bacteria multiply during the ammonia spike?
So the assumption would be: Bacteria dies (possibly due to chemical changes) -> ammonia spike and/or lack of oxygen killing all fish and my snail. Does it then make sense that the shrimp all survived? Are they more resistent to ammonia spikes and/or need less oxygen?

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On 7/5/2023 at 1:05 PM, Max said:

shrimp all survived? Are they more resistent to ammonia spikes and/or need less oxygen?

I have found that since my shrimp are long accustomed to my water and I’m probably 100+ generations in my shrimp are now like cockroaches and could survive nuclear holocaust. I’ve found them in pail bottoms with plant discarded cuttings and vacuum mulm a week or two later no filter nothing. They become a thriving colony if left alone. I’ve done full tank flushes and dropped clipping in a brand new tank and nothing phases them anymore including the extreme ammonia in the muck buckets. 

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