Sudden Death Of All Fish - Temperature Change Impact?

[Sampton]

Hi, We had a 70 litre tropical freshwater tank with a variety of top middle and bottom fish including some hardy angel fish.
Our suburb had a notified power outage a couple of weeks ago for 6 hours. In the 24 hours followng this we lost the entire tank of fish, apart from one bottom feeder catfish (who is now my hero).
This was devastating; most of the fish we had had for 2-3 years without any sickness.
We took the water for testing and it was marginally high for ammonia but not critically so.

Does anyone have any knowledge on whether a water temperature drop could have such a significant impact on all the fish?

We have replaced the tank water, waited a couple of weeks and hope to slowly repopulate the aquarium, commencing today. I'd also appreciate people's advice on how many fish you can host comfortably in a 70L tank (sorry - don't know what that is in gallons for UK/US folk).

Thanks in anticipation.....

 

[Gvilleguy]

Sorry for your loss. Any idea how much the temp dropped? Going with the simple rule of thumb for stocking, you could have around 18 inches of adult fish in your 18 gallon. But tank shape also comes into play due to surface area available for oxygen exchange at the surface. Do you know the tank dimensions?

 

[Sampton]

Thanks for your response Fish Herder. It dropped from 26 (78F) to probably around 20-22 (68F-72) in that time - as it is still end-of-summer here in Australia. Not considerably dramatic.
I'm not understading your formula for fish density....my tank size is 60x30x30cm (around 2x1x1 foot) - what does that equate to in big fish/small fish?

 

[WILDER]

Sorry for your loss. R.I.P.
 
If the temp dropped down really fast it can lead to stress, shock and also lead to problems like swim bladder, whitepot, columnaris.

 

[Munroco]

Thats not a dramatic drop. I'd be surprised if that was what killed your fish.

 

[fluttermoth]

It's much more likely that it was a build up of ammonia that killed your fish, rather than temperature.
 
You said the ammonia was "marginally high for ammonia but not critically so"; I don't know if it was the shop that told you this, but there is really no safe level for ammonia. Even a trace can affect fish enough to kill them.
 
As for restocking your tank, I wouldn't like to recommend species without knowing how hard or soft your water is. You're only going to be able to have small fish, in a tank of that size though. No more angels, please. Your tank is at least half the size you need to house angels comfortably.

 

[Baccus]

The temperature drop should not have caused death outright since it was not as drastic as going from say 24 degrees down to 5 degrees, but the shock of a few degrees and then sudden rewarming once the power resumed could have caused enough shock to allow secondary illnesses to crop up.
 
A 70L tank is really not large and can be trickier to stock with suitable fish. For a tank like yours that is 60x30x30 I would steer well clear of live bearers such as guppies, endlers, platties swordtails mollies or sailfins (mollies and sailfins can get to big for the tank in my opnion any way), unless you are willing to only keep a group of males, otherwise having females in the mix will have you running out of room in the tank in no time thanks to the seemingly never ending supply of fry.
I would try going for some of the dwarf species of fish which can be just as colourful and active without requiring so much room.
without knowing your other water parameters I can only give you a rough list of potenitial fish that you will need to match to your tastes and their water requirements.
Australian Native fish
Spotted Blue Eyes
Delicate Blue Eyes
Almost any native shrimp such as Blackmore River shrimp, Chameleon Shrimp, Riffle shrimp, but avoid all macrobachium shrimp.
 
Non Native Australian fish
Cross banded danio
Rasbora maculata
Sparkling gourami
croaking gourami
pygmy catfish
dwarf catfish
otocinclus
soriety of female siamese fighters
 
these few suggestions are no where near all that is out there but should give you an idea of suitable sizes of fish for your tank. Many fish like to school or loosley shoal so by having smaller species in a tank you can give them the numbers of their own kind to help them feel secure and display their true habits.

 

[Byron]

I agree with the general thinking here that while the temperature was likely a factor (causing stress) it was more likely the water quality that killed the fish.  A 70 litre (20 gallons) is a small space, and without knowing how many fish and at what sizes, I am suspecting the tank was overstocked.  Angelfish are certainly not suitable in a tank so small, regardless.  The filter and water changes (and perhaps live plants?) may have kept things "safe" but when tanks are overstocked (which can involve the fish species as well as their numbers) it is very easy for things to worsen very fast.  The ammonia is a sign this occurred.
 
Plan out your re-stocking carefully, keeping in mind this is a small volume of water.  Some fiish need a group, not all fish are suitable in the same water, etc.  And when taking water to a fish store for any tests, always insist they give you the number.  Without knowing the exact number for any test, it is usually difficult for others to give advice.
 
Byron.