Re: [RML] Designer Fish

Doug Collom (dcollom at
Sat, 14 Nov 1998 23:07:19 +1000

Yes Bruce you are right, we would have to ask more learned heads for expert
advice on this one.

Its very difficult to be a learned head on biological filters in cooler
water here in Queensland. I mean, winter fell on a Thursday this year, and I
was busy that day.

My very basic understanding is that while dissolved oxygen is increased in
cooler water, it doesn't have any great effect on the bacteria, which
function better in the 20s, and apparently physically just don't appreciate
cooler temperatures. That's in a well maintained system of course, if the
filter is already a bit anaerobic, an increase in dissolved oxygen at lower
temperatures could be expected to have more impact.

Whether exactly the same bacterial strains are in filters here in the
sub-tropics, as are in filters in cool-temperate regions is also something I
don't know. Andrew may well have bacteria down his way that tolerate cooler
temperatures better than ours.

You have had me raking through references today, but so far I have not put
my hands on what I'm after, except for a reference by a Dr David D. Sands,
of the Aquarian Advisory Service in Britain, that bacterial systems
generally work better in warmer water, with peak efficiency at 25 degrees C.

I've seen some material fairly recently which suggested that both fish and
bacteria which were kept in constant water temperatures for lengthy periods,
(heated tanks) handled drops in water temperature poorly, compared to
specimens which had experienced regular temperature fluctuations (unheated
tanks). However I haven't found that again yet.

Maybe some of the NSW/ACT Koi pond keepers would know more. Know any Andrew?

Is there a bacteriologist in the house?

Doug Collom

-----Original Message-----
From: Bruce Hansen <bhansen at>
To: rainbowfish at <rainbowfish at>
Date: Saturday, 14 November 1998 12:38
Subject: Re: [RML] Designer Fish

>I wonder if that is so Doug - I thought that the big factor in UGF's is
>aerobic activity and that oxygen dissolves better at cooler temperatures.
>my mind that would translate into better biological activity when cooler
>than warmer. I guess there is an optimum temperature range for this process
>but would have to ask more learned heads for the figures :)
>Bruce Hansen, A.N.G.F.A., Advancing Australian Aquatics.