swimbladder cherry barb, 2/3 Otocinclus affinis are gone :(

[AoiGSR]

I came home tonight and found the following in my 20 gallon:

2 dead Otocinclus affinis (one from my 40 gallon to the 20 gallon and one I just bought last week)

1 Otocinclus affinis that looks like it has swim bladder (still a baby but bought from last week)

1 male cherry barb that wiggles when it swims.

other fish seem okay (4 Brilliant Rasboras, 2 corys and 3 other cherry barbs)

I did a water change this past sunday (5 gallons) and i thought everything was going well.

mostly my cherry barbs have been dying (I replenished 2 2 weeks ago)

i have 1 cherry barb that I saw trying to rub it's body on the gravel.

0 ppm Ammonia
0 ppm Nitrite

pH is between 7.6-7.8


i have no live plants but have algae that i've seen the otos eating and supplement with algae wafers.

I have 1 rena-air air pump pumping in bubbles.

my 20 gallon tank is near a gas fireplace (and sometimes I think I smell a little gas but not sure).

My 40 is right near my 20 but more away from the fireplace.

driftwood is available to soften the water and for the otos and corys.
using emperor power filter.
temp is about 75-77 degrees


is it possible the air that is coming into the water is partially that natural gas?
any suggestions?

-Aoi

[Fishboy-from-NY]

Yes, that can be very deadly.

[Allivymar]

Hiya AoiGSR and welcome to Aquariumadvice.

Are there any signs/symptoms other then the fish dying (changes in behavior, color, breathing, etc). I notice one of the new barbs is scratching itself and the oto has a swim bladder problem; I wonder if the new fish (either the barbs or the oto) brought disease with them. Did you QT them prior to adding them to the tank? Or its possible there was disease in the tank previously and its now really taken hold as you did have probs prior to the additions.

It could be gas, but I get the feeling there have been odors of gas long before fish started dying. I tend to think its disease.

[AoiGSR]

It's kinda weird because the ones that seem to have lived forever are the Brilliant Rasboras. I have to for sooooooo long.

I did not quarantine these fish (replacement barbs and 2 otos). Originally, I was going to use this 20 gallon tank as a quarantine tank when I had the 40 gallon (still have that but wanted to redo that tank with cichlids). Maybe I need to add real live plants in here again? I have some fake ones as this could have served as a hospital tank as well.

Maybe I need a 10 gallon quarantine tank as well?

the other oto has died today the one oto I had was from my 40 gallon and was doing well, but then 2 days ago, they died. followed by the one today.

The one male cherry barb has some fin rot but hasn't gotten worse. I think it's had this for quite a while. This is the cherry barb hat is acting like it is trying to swim to the top but gravity or something is pulling it back down. The cory's seem okay but maybe corys and brilliants can live through any kind of h20.

my LFS said it is probably because I had put too many fish into this tank when I moved from the 40 gallon to the 20 gallon and the tank was not fully cycled. The levels of Nitrite and Ammonia seem okay but I wonder if there is anything else I can check.

I put more drift wood from the other 40 gallon tank to make caves and a place for the otos to stay.

Maybe I should grow plants again and don't use the airpump to bring in o2?

I'll read on this forum to see if I can find anything as well.