Energy efficient aquaria

Hi guys,

Given the current concerns about climate change, we're getting serious
in my household about reducing out energy use . We don't own a car,
and we're renting our flat (so solar hot water etc is out). We've
swapped all our light bulbs for compact fluorescents, and bought a
nice, old fashioned fan for the living room so that we don't have to
use the airconditioner.

We've identified our fish tanks as a large energy sink. We have a 350
litre community tank in the living room, and a pair of 100 litre tanks
in our bedroom. I've done a quick and dirty estimate of their power
usage, as follows (using
http://www.kernsanalysis.com/HeaterCalculator.cgi to calculate heater
power):

Main tank:

Heating - 110W - 964KWh/annum (120x48x60cm tank with 10mm walls
heated to 8 degrees C above ambient (discus))
Lighting - ~200W - 876KWh/annum (2 x 55W CF + 2 x 36W T8 on
electronic ballasts)
Filtration - ~10W - 88KWh/annum (Eheim canister)

Small tanks:

Heating - 150W -1314KWh/annum (Two 60x35x45cm tanks with 6mm walls
heated to 8 degrees C above ambient (discus))
Lighting - ~50W - 219KWh/annum (One 36W T8 on magnetic ballast
shared across both tanks)
Filtration - ~10W - 88KWh/annum (Two small Eheim canisters)

The whole lot adds up to 3.5MWh/annum, or 1.5 tons of CO2 each year,
which is pretty scary.

Anyway, I've been toying with ideas to reduce energy usage. Firstly, I
think I'll remove the T8 fluoros from the big tank, and put AH Supplies
reflectors on the 55W compacts. I calculate that the increase in
reflected light will pretty-much make up for the decrease in power. I
can then knock a few watts off the T8 on the other two tanks by putting
it on an electronic ballast.

After that though, it gets hard. My next thoughts are to double-glaze
the tanks. If I get some 3mm window glass cut, I could space that a
few millimetres off the main glass. It's difficult quantifying what
sort of power saving I'd get, but I'd guess something like 50% is
doable...

Has anyone tried double glazing? Any other ideas?

Cheers,

Suzy