"Mark" wrote in message
...
It is often said on these NGs that the sound of the pump is small
compared
to the sounds in a fishes natural environment. Being an advanced PADI
scuba
diver I'm fortunate to have tested this theory out a few times and
personally I'm not convinced that this is true. Although sound
underwater
travels a long way, it also decays quickly with distance. So, it is
easy to
hear a boat from miles off, but it is relatively quiet until it gets
close.
In fact, I'd descibe the underwater world as remarkable peaceful. I
compare
this to the noise I heard when I put my ear to the fish tank and even
though
the pump is quiet in the air, it sound like a pneumatic drill once my
ear is
in contact with the glass and to me much louder than the fishes natural
environment - probably due to the proximity of the pump. In addition,
the
sea noises are intermittent and random, unlike the constant buzz of the
pump. Now I don't want to get into a discussion about different tanks /
pumps / fish etc, I'm really thinking generically here...

Finally, someone who agrees with me. Aquariums are far noisier
environments than they should be. Much of the pneumatic hammering is
from your airstone and may have very little in common with the audio
volume from your airpump. Multi-diaphram pumps would be better if they
operated in sequence, but they operate in tandem, in opposite directions
(to reduce pump vibration) which probably worsens the effect inside the
tank. Whatever air pump you choose to use a damping chamber would
probably help, but it hasn't been invented yet (sealed 300cc container
with airline connections on either end and loose baffling material
inside).

1. Are the different sound volumes simply a trick of my brain (in the
same
way that a room always look much brighter from the inside than the
outside
because the brain "compensates")? Indeed, has anyone done any decibel
measurements to quantify this?

Excellent question. I'm sure the glass's harmonic frequency is
attentuating and amplifyng different frequencies. I don't have anything
capable of measuring dbAs underwater.

2. Is this constant droning harmful / torture to the fish? (I have seen
it
written that "they look peaceful", but perhaps a visiting alien would
describe a man in a padded cell wearing a straitjacket as "looks
peaceful"!)
I don't know how it would be measured, but again I'm interested in
scientific studies on this.

Because fish use 2 systems (lateral line and inner ears), it's hazordous
to extrapolate too much from our own senses's experiences. A steady
vibration of any significant amplitude will damped their ability to
communicate with movement. This is easily seen with cichlids schooling
fry. The lower the artificial vibrations, the tigher they can maintain
control on sometimes 100s of fry. Add an airstone, and the fry go off in
every direction, with exhausted parents chasing them down.

There is a lot of other communication through vibration used by fish, and
they are essentially being deafened in 'loud' tanks. Another example is
any fish which is a nocturnal hunter would be significantly handicapped
by the 'noise'.

Another example occurs when you drop an airstone into a mbuna tank. You
would normally observe a significantly higher level of activity and
appetite. I suspect that this occurs because they can no longer 'hear'
potential attackers coming, so they compensate with vision, by keeping in
more constant motion (and the greater appetite is to support the higher
energy output).

In regards to the potential for harm with constant droning, I suspect
that besides the dampening effect it has on their own perceptions, that
the drone gets accepted, much like we don't hear white noise. This is
illustrated by their 'deer in the headlights' reaction when you turn off
all sources of vibrational noise. They are momentarily deafened by the
silence.

To minimize the effect, use quieter filters (ie: canisters, submerged
water return, etc), sound dampening materials (plants, wood, rockwork),
larger tanks, low fish-loads and avoid fish which are particulary
susceptible to noise (ie: ID sharks).

NetMax

BTW, I did come across one site that had lots of info on the effects of
particular types of sounds (sonic booms, infrasound etc.) on fish, but
it
was all "big scale" stuff and there was nothing on the effect on the
_constant_ buzz produced by a pump on a fish tank.

Cheers (and sorry for the long posting!)
Mark