Mysterious Fish Killer (w/o Bad Water Quality) in Cycled Tank

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Bluenavyguy

Aquarium Advice Newbie
Joined
Jan 24, 2018
Messages
1
Hello*everyone!

I have a 20 gallon, tropical, freshwater aquarium that has cycled for three years. However, my aquarium has unexpectedly developed issues that I am unsure how to solve.

The problem started after I bought a Harlequin rasbora from the local aquarium store. I assessed the fish to assure that it had good health. Satisfied with its behavior, I took the fish home and started my acclimation protocol. I acclimated my fish to 75 degrees Fahrenheit by immersing the store bag in my aquarium. Every 10 minutes, I added one tablespoon of aquarium water into the bag as to acclimate my fish to the aquarium's chemistry. After 30 minutes of acclimation I poured most of the bag water down the drain. Only my fish and one tablespoon of bag water entered the aquarium. The new fish showed no signs of distress and schooled with my other Harlequin rasboras. Then, two days later, it died without any signs of injury.

Since then, my fishes have successively died from “unknown" causes. Each fish swam and ate normally before death. No fish displayed signs of illness or injury - except for a skirt tetra with excessive fin rot. I doubt that infection caused the problem though. I treated my aquarium fishes with API Melafix before adding the new Harlequin rasbora. An overdose of melafix seems unlikely as well, since*I performed two 30% water changes (one week apart) after the five-day medicine treatment. Also, I reinserted the carbon filtration to ensure that no melafix remained in my tank.

After three more fish died, I decided to retest my water chemistry parameters one morning. I used two methods for assessing my tank's water chemistry. I used an API Test Strip kit to measure the pH and hardness inside my aquarium. Then I used an API Freshwater Test kit to measure the pH and nitrogen waste levels. Both kits indicated that pH, hardness, NO2, and NH3 levels were within acceptable parameters for tropical aquarium fishes. Nonetheless, another fish died later that evening.

I urgently need help solving this issue. Fish that die without any reasonable cause does not occur. However, without any signs of illness and great water chemistry, I am at a loss of how to identify the mysterious “killer”. Any other ideas of what I can do to prevent further deaths?
:thanks:
-Bluenavyguy
 
Hello*everyone!

I have a 20 gallon, tropical, freshwater aquarium that has cycled for three years. However, my aquarium has unexpectedly developed issues that I am unsure how to solve.

The problem started after I bought a Harlequin rasbora from the local aquarium store. I assessed the fish to assure that it had good health. Satisfied with its behavior, I took the fish home and started my acclimation protocol. I acclimated my fish to 75 degrees Fahrenheit by immersing the store bag in my aquarium. Every 10 minutes, I added one tablespoon of aquarium water into the bag as to acclimate my fish to the aquarium's chemistry. After 30 minutes of acclimation I poured most of the bag water down the drain. Only my fish and one tablespoon of bag water entered the aquarium. The new fish showed no signs of distress and schooled with my other Harlequin rasboras. Then, two days later, it died without any signs of injury.

Since then, my fishes have successively died from “unknown" causes. Each fish swam and ate normally before death. No fish displayed signs of illness or injury - except for a skirt tetra with excessive fin rot. I doubt that infection caused the problem though. I treated my aquarium fishes with API Melafix before adding the new Harlequin rasbora. An overdose of melafix seems unlikely as well, since*I performed two 30% water changes (one week apart) after the five-day medicine treatment. Also, I reinserted the carbon filtration to ensure that no melafix remained in my tank.

After three more fish died, I decided to retest my water chemistry parameters one morning. I used two methods for assessing my tank's water chemistry. I used an API Test Strip kit to measure the pH and hardness inside my aquarium. Then I used an API Freshwater Test kit to measure the pH and nitrogen waste levels. Both kits indicated that pH, hardness, NO2, and NH3 levels were within acceptable parameters for tropical aquarium fishes. Nonetheless, another fish died later that evening.

I urgently need help solving this issue. Fish that die without any reasonable cause does not occur. However, without any signs of illness and great water chemistry, I am at a loss of how to identify the mysterious “killer”. Any other ideas of what I can do to prevent further deaths?
:thanks:
-Bluenavyguy
What was you ammonia & nitrite readings as they should always be zero, as far as the new fish it probably brought in a sickness, a strain of columanaris possibly which there are strains that you cannot see, also melafix you should just throw away it is toxic and does nothing really except for maybe a wound, I have had people say it works great but in my experience it did nothing but smell up the tank and I was able to do better with more frequent water changes to keep the water pristine.

If the tanks not planted I would do 50% water change and slowly add in a bit of dissolved aquarium salt that's been dissolved in treated conditioned water , not a lot just a bit, if your fish are dying without symptoms it could be a build up of melafix (toxic) or columanaris or another illness.

Do a 50% water change, don't add no more melafix, rinse filter pads/sponges in aquarium water that you syphoned from the tank (not tap water), add a half dose of aquarium salt (1 tablespoon per 5 gallons so I would do 1 per 10 make sure it's dissolved before adding it), lower tank temp to 74-76 fin rot spreads faster at higher Temps, the truth of the matter is clean water will do more for your fish than salt /melafix will do you could opt to not use anything and just keep the water ultra clean and it should get better.

Do you have pics of the fish with the fin rot?
 
Quick unrecognizable deaths usually spell columnaris to me..
Here is one good link to check out ...
https://r.search.aol.com/_ylt=A0LEV...118.html/RK=0/RS=LAtziQiROXYml9g1ORxlX4viPTY-

Your skirt with fin rot could be the culprit..I agrre with Ricks assessment of the 'fixes' ..Useless on more then a scratch.. It is the 'mis labled ' Bactine of aquarium meds IMO..Columnaris needs antibiotics and Seachems Kannaplex and APIs Furan2 are the choice combined ATM..Mis use of antibiotics has led to many no longer working at all on this issue...
Good luck and let us know if you think strain 2 matches up...
 
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