My Danio Problem

I had recently about three weeks ago added 7 zebra danios to my 20 gallon long aquarium. The tank included a dwarf gourami, 4 platies and 2 bosemanI rainbows. Over the course I have lost four of the danios and I do not know why. I lost two the first week and then one the second week and one early today. At first I thought it was swim bladder poisoning, but I do not know for sure. I have well water so there’s nothing in the water that could poison the fish and I have been adding water conditioner frequently. If anyone has advice I would be open to anything

 

Can you post your water parameters? Temperature, ammonia, nitrite, and nitrate?

Also, those bosemanis will eventually need a 55 gallon.

 

Yes I am going to purchasing a 55 gallon in a couple of days. The tank is about 75 degrees and the ph is 7.0. The strangest thing about my problem is that the only fish that have died on me have been those danios and they are know to be hardy fish.

 

Yes I am going to purchasing a 55 gallon in a couple of days. The tank is about 75 degrees and the ph is 7.0. The strangest thing about my problem is that the only fish that have died on me have been those danios and they are know to be hardy fish.

Can you post your other parameters? How old is the tank?

Also, where did you purchase the Danios?

 

Can you post your other parameters? How old is the tank?

Also, where did you purchase the Danios?

I am not curently home right now so I do not know any of the other parameters. The tank has been running for about a month now but it is 20 years old and the filters brand new. I got the danios at a petco.