On Sun, 15 May 2011 18:10:59 +0100, Chris Hogg wrote:

Whilst at the Glasgow branch of Dobbies last weekend , I had a
chat
with the fish salesman and he said without doubt in order to keep
fish
healthy in our present climate, I need an electric filter /
oxygenator
and pond heater. Goodness !

Hum, when I was a lad we kept a goldfish in a tank on the side board
with no filter, lights, heater etc. Seemed happy enough. No.1
Daughter now has a cold water aquarium with filter and airator,
(limited light to stop it going green) though the Hill Stream Loaches
keep the glass stones ornaments pretty clean. The fish we had when I
was a lad would just sort of drift about slowly, these ones zoom
around all over the place. So I guess they are in a better enviroment
but getting that enviroment established with the ammonia nitrite
nitrate process is a right beggar.

He reckoned the levels of ammonia built up in the pond whilst it
was
frozen as the toxic gas had nowhere to escape to and thats what
killed
my poor fish.

I have my doubts. I think the salesman is moving indoor aquarium
keeping to small outdoor ponds and that may not be the correct thing
to do. One assumes these fish have otherwise been happy and the
others in the area that also died and that all have survived previous
winters.

Whether your fish died from the build-up of toxic gases or whether they
just froze solid, I don't know,

If they survived previous winters I'd go for simple frozen to death,
either by the actual cold going to low or just the period of cold
being too much.

Goldfish are very inactive in cold weather, and I doubt that much
ammonia is produced, although I may be wrong.

IIRC the ammonia is fish wee, as you say very inactive when it gets
cold, so little ammonia produced.

But I would be inclined to investigate a low-wattage heater to stop it
freezing solid, preferably one fitted with a thermostat that you can
set at a few degrees above zero so that the heater's only on when
there's a real danger of freezing.

I wouldn't, it'll tend to make the water circulate and unless you
pump in enough heat to make up for all the losses I suspect a
partially heated is more likely to freeze solid. Water has it's
highest density at about 4C so colder water will tend to float on top
and freeze, ice is also a reasonable insulator. Ponds and lakes
rarely freeze more than a foot thick in this country.

Personally I think it was just the extreme cold for an extended
period that killed the fish. Just one of those things I'm afraid.

--
Cheers
Dave.