Fish keep dying in two tanks.

[IFLAquatics]

I had 3 bichirs and the only one that survived the water change last night was the largest and he had to be evacuated into a cichlid tank temporarily. This is a problem we have had in the past and we cant figure out why. 75 gallon tank, left filter media intact, cleaned out sand (large pleco dead now but was a massive waste contributor.) We took the eels and pleco out because the last time we tried to do a water change something killed half the fish in the tank also. They did great in a little quarantine for the 2 hours with a large air stone. So i took only decorations out and rinsed them only in hot water, we drained the tank to nothing, cleaned the sand and drianed it again until the water was somewhat clean in comparison to the black mass that was there. i know you arent supposed to do all that but the tank had gotten out of hand. Ive done this 5 or 6 times before with other tanks of ours and have never had fish loss in any tanks but this tank and a 20 gallon. I seem to be running into a problem with something that has to do with their gills because all of them start sliming up really bad and then have difficulty breathing. The water is conditioned, treated with bacterial treatment to prevent fish loss. Its petco brand bacterial booster. We have used this in the same way in extreme cases because of circumstances that left us unable to clean the tanks as often. Their slime coats go crazy, eyes glaze over, breathing starts to get difficult, even with their lung the bichirs almost didnt make it. Also API water conditioner. All water levels pristine except hardness. Conditioned tank before replacing fish, bacteria, everything. The 20 gallon we had only killed our catfish. They died without a water change though. We lost 4 striped and 2 spotted raphaels 1 pleco and an irridescent shark. All were in process of quarantine on different water cycles with different filter media almost every time. But we use the 20 for a baby savannah monitor now so what does everyone think about this? I cant stand losing my fish bcause they are like my kids and i need to figure out what this slime cloud gill strangling goo is. I noticed the water seems almost like someone had spit in a cup of water, almost like algae but with absolutely no color. Almost lik a froth in the water and the surface looked clear as day but swampy. Idk how to explain it.

 

[tlindsey]

I had 3 bichirs and the only one that survived the water change last night was the largest and he had to be evacuated into a cichlid tank temporarily. This is a problem we have had in the past and we cant figure out why. 75 gallon tank, left filter media intact, cleaned out sand (large pleco dead now but was a massive waste contributor.) We took the eels and pleco out because the last time we tried to do a water change something killed half the fish in the tank also. They did great in a little quarantine for the 2 hours with a large air stone. So i took only decorations out and rinsed them only in hot water, we drained the tank to nothing, cleaned the sand and drianed it again until the water was somewhat clean in comparison to the black mass that was there. i know you arent supposed to do all that but the tank had gotten out of hand. Ive done this 5 or 6 times before with other tanks of ours and have never had fish loss in any tanks but this tank and a 20 gallon. I seem to be running into a problem with something that has to do with their gills because all of them start sliming up really bad and then have difficulty breathing. The water is conditioned, treated with bacterial treatment to prevent fish loss. Its petco brand bacterial booster. We have used this in the same way in extreme cases because of circumstances that left us unable to clean the tanks as often. Their slime coats go crazy, eyes glaze over, breathing starts to get difficult, even with their lung the bichirs almost didnt make it. Also API water conditioner. All water levels pristine except hardness. Conditioned tank before replacing fish, bacteria, everything. The 20 gallon we had only killed our catfish. They died without a water change though. We lost 4 striped and 2 spotted raphaels 1 pleco and an irridescent shark. All were in process of quarantine on different water cycles with different filter media almost every time. But we use the 20 for a baby savannah monitor now so what does everyone think about this? I cant stand losing my fish bcause they are like my kids and i need to figure out what this slime cloud gill strangling goo is. I noticed the water seems almost like someone had spit in a cup of water, almost like algae but with absolutely no color. Almost lik a froth in the water and the surface looked clear as day but swampy. Idk how to explain it.

Sounds like old tank syndrome. Did you get any odor from the sand while you were removeing it?

 

[dan518]

What is the full stocking on the tanks
What is the filtration,
How much and how often for the waterchange.

 

[IFLAquatics]

What is the full stocking on the tanks
What is the filtration,
How much and how often for the waterchange.

To be honest, the water changes have been a 60% water change which was after transporting the tank with water in it almost a month and a half ago And then one 40 percent about 2 and a half weeks ago. Its a penguin on their, 75 gallon filter, one 12 inch polypterus senegalus (i believe) bichir, one 3 inch albino bichir and one 3 inch polypterus senegalus bichir and one 10 inch albino common pleco

 

[IFLAquatics]

Sounds like old tank syndrome. Did you get any odor from the sand while you were removeing it?

I have never heard of that but im about to look into it. And yes the tank always smells like rotting teeth from the sand. (Sorry for the messed up comparison but thats the best i can get)

 

[IFLAquatics]

Sounds like old tank syndrome. Did you get any odor from the sand while you were removeing it?

I did a little reading into it but im not seeing it doing what i said unless it can happen instantly from the sand being shifted, i kept it well ventilated, filter on with a 14 inch aerator stone.

 

[MrsE88]

Wait, so only 2 water changes in a month and a half?

What are your test results?
How often are you feeding? And what are you feeding?

 

[dan518]

With that stocking I would be doing a minimum of 50% every week with a good substrate vac. From your reply it sounds like the tank is only getting a 40% every 17 days unless I am reading it wrong.

 

[tlindsey]

I have never heard of that but im about to look into it. And yes the tank always smells like rotting teeth from the sand. (Sorry for the messed up comparison but thats the best i can get)

The downside of using sand sits stagnant it will develop pockets of sulphuric gases which are toxic to fish. It will have a rotting egg smell.

 

[Rocksor]

I have never heard of that but im about to look into it. And yes the tank always smells like rotting teeth from the sand. (Sorry for the messed up comparison but thats the best i can get)

Sounds like you have anaerobic bacteria in the sand where you have denitrification happening, basically a conversion of organic matter to nitrate and then into nitrogen. When you do a water change, the sand is getting stirred up, and exposing the anaerobic bacteria oxygen. This will disrupt the denitrification process, and release nitrite and/or ammonia into the water column.

This tank isn't planted right?

What type of filtration do you have?

How deep is the sand?

Are you vacuuming to the bottom of the sand?

What type of sand?

And you're not doing weekly water changes? If so how much?