Fish dying

Hello, I have a 20g tank initially setup in June 2022. I stocked with 12 glofish tetra and 2 plecos. After 3-4 months the fish started swimming weirdly and died one by one. After 6 months of setting up I realised that the water I was using had high ammonia. Then I changed the water source. At that time I was left with 4 glofish only. Once I was confident that the new water source had stabilized and the tank was always having good water parameters, I added 4 more glofish (2 were small - only 1 inch), 2 thick lipped gouramis and 2 nerite snails.

From this last batch, one new small glofish died the day I introduced her in my tank. One gourami died within 2 weeks without any symptoms. One snail fell from the glass and died. Within next 2 months the other new small glofish and the other gourami died (gourami was sluggish for 2-3 days before dying and its belly got darkened - see photo). Also, all the previous remaining 4 glofish died. One of these had its mouth stuck open (see photo - yellow one).

Water parameters are all fine (ammonia, nitrite, nitrate, ph tested using API).

Can anybody identify the problem?

What's you pH level? Do you have cover for the gourami's to hide under?

Ellie Potts said:

What's you pH level? Do you have cover for the gourami's to hide under?

Click to expand...

Ph stays at about 6.8 - 7.0
There is a rock kind of an article that is hollow inside with open top and a few openings like eyes on the sides. The gouramis loved hiding inside that (see pic - the dark one right in the center).

Have you considered adding the plant salvinia? A floating plant might help with your Anubias issues and would get your gouramis more comfortable. Frogbit or water lettuce are good too.

but that would not explain the sudden deaths. What're you feeding and how often are you doing water changes? I would also suggest adding fish a little bit more gradually.

Ellie Potts said:

Have you considered adding the plant salvinia? A floating plant might help with your Anubias issues and would get your gouramis more comfortable. Frogbit or water lettuce are good too.

but that would not explain the sudden deaths. What're you feeding and how often are you doing water changes? I would also suggest adding fish a little bit more gradually.

Click to expand...

I have been wanting some floating plants but they were not available. Will continue searching.

Feeding them mostly flakes and sometimes bits. Could this be a problem? Should I change the brand?

Water change every 7-10 days, 50%.

Now that I am left with only 2 tetras and one snail, am planning to add more fish and another snail. Would like to have a total of 8-9 fish and 2 snails in the tank. Will add in 2 lots I think.

If your fish keep dying, adding more fish will result in more deaths.
I'd go to the pet store and ask for a sample of water from the fish tank you're interested in buying and test it for pH and GH. Compare it with your own tank water to see if they are similar.
Do other fish keepers in your area use the same source of water as you do?
I assume your tank has good water movement, enough dissolved oxygen levels?

I now use the normal minicipal water. Most fish keepers are also using this.

Water movement is fine. How can I check dissolved oxygen levels? I assume it should be fine with the live plants in there.

Vikasr said:

I now use the normal minicipal water. Most fish keepers are also using this.

Water movement is fine. How can I check dissolved oxygen levels? I assume it should be fine with the live plants in there.

Click to expand...

A good rule of thumb is the more surface agitation the higher the oxygen level.

I assume the oxygen levels should be fine

Vikasr said:

I assume the oxygen levels should be fine

Click to expand...

Yes, I see a filter in your photo so it's fine. Apart from things already mentioned, is your temperature within 22C -27C?

TNG said:

Yes, I see a filter in your photo so it's fine. Apart from things already mentioned, is your temperature within 22C -27C?

Click to expand...

Yes temperature is around 26-27C.

This is such an odd mystery. I agree adding in more fish while the tank is acting like a death trap may be unwise, but not sure what is going on. Do you have a second tank that could act as a quarantine tank? Any other fish you're interested in or a different local store? Maybe you're buying them diseased? Not sure.

Ellie Potts said:

Do you have a second tank that could act as a quarantine tank?

Click to expand...

No, I dont.

Ellie Potts said:

Maybe you're buying them diseased?

Click to expand...

This has come to my mind. I bought the first batch of 12 glofish from one store and the first died after 3 months and the last 2 died after 9 months. This was when initially for the first 7 months I was, without knowledge, using water that had 1.5ppm ammonia that settled down to 0.25ppm in a few days in the tank and never got to 0ppm. Most of these 12 glofish died showing ammonia poisoning symptoms. And this is the store where I have seen a few other fish keepers buying their fish from, although this store is kept really dirty by its owner and does not have much variety of fish.

The second lot of 4 glofish and 2 gouramis were bought from another store, after my ammonia problems were fixed and water parameters (ammonia, nitrite, nitrate, ph) were good and stable. Out of these 6 fish, 4 died within 2 months and 2 I still have.

So this does give me a feeling that the fish from the second store had some disease or were not able to live due to something unknown.

Vikasr said:

No, I dont.



This has come to my mind. I bought the first batch of 12 glofish from one store and the first died after 3 months and the last 2 died after 9 months. This was when initially for the first 7 months I was, without knowledge, using water that had 1.5ppm ammonia that settled down to 0.25ppm in a few days in the tank and never got to 0ppm. Most of these 12 glofish died showing ammonia poisoning symptoms. And this is the store where I have seen a few other fish keepers buying their fish from, although this store is kept really dirty by its owner and does not have much variety of fish.

The second lot of 4 glofish and 2 gouramis were bought from another store, after my ammonia problems were fixed and water parameters (ammonia, nitrite, nitrate, ph) were good and stable. Out of these 6 fish, 4 died within 2 months and 2 I still have.

So this does give me a feeling that the fish from the second store had some disease or were not able to live due to something unknown.

Click to expand...

Yes, I would try the original place or even somewhere entirely new with just 1-2 fish and see what happens.

Ellie Potts said:

Yes, I would try the original place or even somewhere entirely new with just 1-2 fish and see what happens.

Click to expand...

Good idea. Will try 2 fish from the original place.