20 G tank with some juvenile Geo Red Head Tapajos (1.50") and juv Cory adolphoi (1.00"). Ammnoia 0, Nitrite 0, Nitrate 30. Filtration is overkill - Eheim 2226 canister + Aquatop PF25 HOB w/ UV sterilizer. Tank has been set up for over a year and these fish have been in there for about 6 weeks. This AM, all fish were breathing rapidly and one Cory perished. I added an airstone immediately while I tested the water parameters listed above. Can anyone speculate what may have occurred?
Fish breathing rapidly/heavily
- Thread starter erik333
- Start date
Yes, I did a water change last night to get Nitrates down. They were approaching 80-100. My tap water is from a well so no chlorine/chloramine, etc.
I am on a well too and have never had the problem but some water lines pick up gases this time of year. Does your water ever look milky? If it does then that is gassing and it is harmful to fish, just like chlorine. Another thing comes to mind and that is did anyone spray anything in the room your tank is in? Just throwing ideas out there.
no... water was clear and nothing was sprayed. The air stone seems to have helped. I had put some live blackworms in this AM and within 20-30 min of putting the airstone in, the geos were back to digging and some corys were doing battle with blackworms. Its strange - I really don't know the answer either.
I see you have plenty of filtration, but how much water surface agitation are you getting?
Maybe a bio film developed over the water surface and hinder O2 exchange.....and the bubbles from the airstone broke that up, allowing O2 exchange again
Maybe a bio film developed over the water surface and hinder O2 exchange.....and the bubbles from the airstone broke that up, allowing O2 exchange again
Xraycer, given all the other circumstances, I think your explanation makes the most sense. I do see an oil slick on top from time to time. I'm not sure where this originates from - maybe the organics in the fish food? The Aquatop UV Filter does have an apparatus that acts as a surface skimmer - but I don't know if its the most reliable piece of equipment. I think this time, i'm just going to keep the air stone in. I removed it before because I thought that the surface agitation between the eheim and HOB were sufficient. But perhaps not.
You can invest in Eheim surface skimmer and direct your filter (or circulation powerhead) water output up toward the surface for more gas exchange and get rip the air stone 
The same thing happened to me a few months ago. Didn't come up with a definitive answer, but I leaned toward temp of new water was off. Or I added too much flourish excel. How close were the temps? Any additives?
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No additives - I don't use them. As for Temps, I can't tell you that I measured it, but I go by feel and the new water was close to tank temp. Also, I've noticed this at other times when water changes were not recent. I've searched a lot online about this and anything I've found points to a disruption in Nitrogen Cycle, which I know was not the case here. I do believe that this was a surface/oil issue of not allowing gas exchange. I did notice the Corys shooting up to the surface for the air gulp much more than they normally do.
