Sudden tank crash

[Smrgle]

I have had a 40 gallon planted tank set up for over two years with angelfish, cardinal tetras, a few elderly guppies, and a pair of bushy nose plecos. Two weeks ago, I took a risk and added four angelfish to replace a few I had lost over the years. Yesterday, fish started dying.

I have lost 1 pleco, 7 cardinal tetras, both guppies, and the only remaining original angelfish. 3/4 of the new angelfish are still alive. There are no signs of distress (clamped fins, wasting, flashing, refusing to eat, etc.), nor obvious disease. One cardinal tetra had an apparent skin lesion, but it survived through the night and into today, while four other fish died during that time. I started the first round of erythromycin and general cure last night. The 9 other tanks in my fish room are functioning normally.

Attached are the water test and fish I have removed but not yet disposed of. Thank you in advance for any help or explanations you can provide.

[Colu]

A little more information would be helpful what's your ammonia level did you quarantine before adding the new fish any lose of colour rapid breathing have you recently do a water change before the deaths if so did you add a dechlorinator any possible of contamination with house cleaning products @Smrgle

Edited March 5 by Colu

[Whitecloud09]

Yeah do you have a way to test ammonia and how long did you wait to cycle the tank @Smrgle? How much do you do water changes, these Qs might seem odd but like @Colu, the more info the better help everyone can be.

[Smrgle]

@ColuI did not check ammonia, but I have no reason to suspect there is any (well established tank, under gravel filter, no odd behavior in surviving fish). I did not quarantine.  Fish kept color up until death, no water change recently, no chlorine in the tank. I don't add dechlorinator when doing water changes, and have not for the past 7 years. 

@Whitecloud09 I do have a liquid test kit, but this tank has been set up for over two years at this point, and is very well seasoned. I am happy to answer questions! I tend to leave out things I don't think are relevant, which is not great here

Edited March 5 by Smrgle

[Whitecloud09]

On 3/5/2024 at 6:56 PM, Smrgle said:

I did not check ammonia, but I have no reason to suspect there is any (well established tank, under gravel filter, no odd behavior in surviving fish). I did not quarantine.  Fish kept color up until death, no water change recently, no chlorine in the tank. I don't add dechlorinator when doing water changes, and have not for the past 7 years. 

I would find a way to check ammonia, you might be surprised, a betta tank I have is very well set up (2 years or more) and I got ammonia a couple of days ago, and I panicked, so I would check to be on the SAFE side of things @Smrgle

If no odd behavior it probably isn’t ammonia but on the SAFE side I would give it a check, tell us what it read and if not this, I have a couple more Qs @Smrgle

[Smrgle]

@Whitecloud09 Ammonia is 0 according to the API master test kit. One dead guppy did have a long white streamer coming out of it's side. No other fish had "burst" although some had been partially eaten. 

[Colu]

On 3/6/2024 at 12:06 AM, Smrgle said:

@Whitecloud09 Ammonia is 0 according to the API master test kit. One dead guppy did have a long white streamer coming out of it's side. No other fish had "burst" although some had been partially eaten. 

With mast die off in a short space of time it's more likely your new angelfish introduced a fast acting bacteria such as columnaris that can kill in 24hr without your fish showing symptoms your new fish could be imumme to and that's why it's not affecting your New fish I would keep treating with erythromycin and get holed of kanaplex it's a more broad spectrum antibiotic treatment I would follow up with a course of that if your still losing fish  and add some aquarium salt 1 table spoon for 10 gallons that will aid Gill function and add essential electrolytes