Help All my angelfish died overnight!

lachjr

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So...This morning I woke up to find my tank full of dead fish.I would really appreciate anyone’s help as to why this happened.

My 4 angelfish, 13 tetras and 1 cory had died overnight. I was devastated and don’t know what happened to the tank. It was fully cycled and had been set up for over a year. I always do regular water changes and have never had anything like this happen in the past.
It is a 300l (75g) tank and was planted, with a sand substrate. Before this incident the tank was stocked with:

15 ornate tetras
11 panda corys
4 Apistogramma Pebas morado
1 Apistogramma Bitaeniata
3 Bristlenose plecos
4 Rio Nanay Angelfish

These fish have been living together peacefully for months now. 9 of these tetras were new, as I bought them about 4 days ago, along with two new led lights.
I did a water change (about 40%) the day before, exactly like I have done every other time. I used tap water, and conditioned it with prime before adding it to the tank. I am also treating the tank for Black Beard algae, and added in 30ml of ‘No more black beard’ to the tank. I also added in a small amount (about 5l) of tannins to the tank. These had been sitting in a container in the tank cabinet for the past week, as the week prior I added magnolia leaves the bottom of the tank.

All the fish were looked perfectly healthy and happy before I went to bed and were acting as normal.

The next morning I woke up to find a scattering of dead fish across the substrate. The remaining cories were swimming up and down the side of the tank, gulping air from the surface and occasionally so did the Bristlenose. The 2 tetras were staying near the surface and the Apistos were very inactive. I immediately took out the dead fish and tested the water and the parameters are as follows:
Ammonia - 0, Nitrate - 40, Nitrite - 0.25, ph - 6.0
The nitrate is normally at 10 and the nitrite at 0.
After a large, 80% water change everyone seems to be back to normal.

My three most likely scenarios are:
  1. The tannins I added had some form of nitrites and nitrates in them.
  2. The water in the tank had become more acidic after adding the leaves and when I put the tap water (ph of 7) in, the ph swing may have shocked the fish.
  3. I have heard stories of build ups of toxic gases under sand substrates, could a sudden release of these gases have killed the fish.
Any help would be greatly appreciated!!

Here’s what the tank looked like:

178F99F4-4F87-4187-96AB-48D4B3818B74.jpeg
Thankyou!!
 

Charlie’s Dad

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I am sorry for your losses. My opinion would be the possibility of built up toxins maybe from the tannins.

It is very troubling and puzzling at the same time when ever just one of our finly friends pass......again I am very very sorry.
 

goldface

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The only thing I can think of that could have such a devastating effect is adding the "no more black beard". What exactly is the formula for that? I'm not entirely convinced with your other likely scenarios.
 

david1978

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DollyDolly said:
Is it possible something leaked electricity into the water?
I would say no since op didnt say the tank bit them getting out the dead fish.
 
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lachjr

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Thankyou everyone,
I am most suspicious about the tannins, as they were sitting under the tank for a couple of days.
The ‘no more black beard’s active ingredient is called polyglutaraldahyde. I haven’t heard of anyone having problems with this product, however it is possibly that I might have overdosed slightly.
I don’t think that electricity would have leaked into the water, because their were fish that survived, and there was no electrical short. Is it possible that there was too much co2 produced because of the new fish?
Thanks again for the replies and support!
 

david1978

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Rebranded excell. Its easily over dosed.
 

AvalancheDave

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lachjr said:
The ‘no more black beard’s active ingredient is called polyglutaraldahyde. I haven’t heard of anyone having problems with this product, however it is possibly that I might have overdosed slightly.
Glutaraldehyde is used as a fish poison. Why it's made its way into so many aquarium products befuddles me.

It's been attributed to anything from tank wipeouts, fin rot, dropsy, red gills, random deaths, etc.
 
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lachjr

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AvalancheDave said:
Glutaraldehyde is used as a fish poison. Why it's made its way into so many aquarium products befuddles me.

It's been attributed to anything from tank wipeouts, fin rot, dropsy, red gills, random deaths, etc.
Thanks, I’ll be more careful using these sort of products in future
 

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