A fatal mistake? Not so fast…

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Not long ago, I thought I had made a fatal fish mistake. My small tanks (< 30g) are filtered with HOBs, with the exception of one that is filtered with a small, external canister. And none of these tanks have back up air pumps for power outages. When I feed the HOB- filtered tanks, I typically turn off the filters, something I did as usual a few nights ago. I do this to prevent food from getting blown around and inevitably getting sucked into the filter intakes even though they’re prefiltered. At the time, I had three such tanks occupied. Two of those each contained a single adult Telmatochromis temporalis, and the third only contained a few juveniles. The two adult Telmats are actually my breeding pair. They’re segregated because they’re prolific breeders and, to be honest, I needed a break from caring for so many fry.

Back to the almost fatal mistake. You’ve probably picked up on my error by now. Yep, I went to bed one night and forgot to restart the filters. Normally, a tank without water movement for oxygen exchange is a death trap. Years ago, I had a filter quit on a heavily stocked 55g tank and I lost 1/3 of the occupants because of oxygen depletion.

Anyway, once I discovered the HOB filters on the three tanks weren’t running, nearly 16 hours had passed. Naturally, I immediately looked in the tanks, expecting to see both adults dead. Astonishingly, both adult Telmats were just fine, and neither of them were at the surface (gasping for air) when I looked into the tanks.

I thought about this event for a long while. All three of those tanks are 20g longs. I wasn’t worried about the juvenile tank. They were too little to be affected by a 16-hour outage. But the outcome of the two adult tanks surprised me. I compared this event to the 55g event years ago. What was the difference?

First of all, the 55g contained numerous occupants. Second, all the livestock were pretty active swimmers. The two Telmats in the 20s are both pretty inactive. They both spend most of their time in the caves that are provided in each tank. I believe it’s the fact that they were sole occupants and inactive that saved them. Even though the male is quite large (~4.5″), he seems no worse for the wear.

I will state for the record that I would not expect two adult Telmats of this species to survive nearly 16 hours in a 20g tank with zero water movement. That was a surprise…and a nice one.


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