Since we are concerned about minimizing the impacts we have on the environment, is the Aquarium a luxury item or something we require?
It is a luxury.
So is all landscaping.......
So is indoor plumbing for that matter.
So are toilets.
For the sake of argument, let's say the Aquarium is not a luxury item and we want to use a Best Management Practice(BMP's).
This is a common acronym used by use ecological Biologist types of which I am one.
What are the main impacts from aquariums? Cost wise anyways that we can minimize?
Lighting, temperature and flow/pumps.
Lighting from the typically 3-4 W/gal down to the 1.5 W/gal range leads to a savings in CA, USA on a 55 gallon tank of: ~35-55$ a year electric cost.
Water? 1400 Gallons, the cost?
Folks waste more than the 27.5 Gallons use for the weekly water per day, about 100-200 gallons here. That's a lot of waste. So do you have a low flow toilet? Water reduction shower head?
Irrigation or water a lawn?
http://www.marinwater.org/
I'll use their lowest Tier 1 rate:
110 Gallon used per month, monthly bill is 31.25$ for 162 Gal use per day, or 4750/4860 Gallon = you saved a whopping 70 cents per month or.........8.40$.
Marin has some of the highest water rates in the USA.
Energy waste?
Well, the electric aspect certainly has a lot more waste associated with it, you cannot do much with wasted lighting..........wastewater is not really waste.
So say you decide to do a BMP for the aquarium, but say....you wanna keep CO2 and say try lower light. Now you run the Biology at it's peak efficacy. This makes CO2 management much easier. And ultimately an easier tank and one that does well over time, since it REALLY IS a LUXURY, we ought to make it fun and not a headache and lots of labor.
So high light should almost never be advised......... period.
Folks on these forums give a FREE PASS to high lighting, but howl over water waste curiously. Fear not, this is not directed at you personally

, a certain plager that routinely bashes EI loves this comment, but if you think through it and look at the logic and critically consider it, it makes virtually no sense, it's called pandering to what you believe rather than what are the facts. Political spin essentially.
I'd argue that Diana's suggestion is about the best BMP you can do over all, but it has limitations horticulturally.
I have such tanks myself and support this method strongly.
I do it with the water column and the sediment.
No water changes.
Her method relies more on the sediment only, some waste from fish etc.
If you wish to accept say one water change once every 1-2 months, then low light + CO2 is good, but you should do larger water changes, not lots of smaller ones, because those remix and you waste the water fraction you could have done doing a single large water change vs several smaller ones.
Pumps: in general, a good environment is produced for larger tanks, say 40 gal or over with a nice high grade pump, and a wet/dry set up. Canisters also offer good energy use, but offer less flow. Good flow has trade offs as well(more energy) but many low pressure high flow pumps are availabel and having a larger sump return pump is not hard to adjust to get just the right amount of flow without using a valve to restrict flows.
Temp, perhaps the largest use of energy.
Reducing the temp down 2-4 degrees can have a huge energy savings.
Do we need sensitive warm water fish? No, not really.
But..again.....trade offs.
Things grow faster and are harder to keep up on, O2 levels are lower at higher temps as well. All things that go against the general philosophy of BMP's.
I view the aquarium much like a farm.
I raise and breed livestock(see Sturisoma fry I recently pulled out), Staorugyne I sell in larger amounts(my crop), Fire red cherry shrimp I sell locally. Other plants from time to time.
I make about 3000-4000$ a year, spend about 1200$.
Not bad.
My water ends up on my ivy and other landscaping weeds.
So instead of using the irrigation system and 1200 Gallon s a week min, I use about 300 Gallons total but with nice non chlorinated tank water with ferts that are dilute and help the bacteria in the soil grow. Chlorinated tap is not good for soil and plants, kills some fungi that attack plants, but kills the good fungi and bacteria also.
You can chose to focus on one issue or take a more critical approach to BMP's.
This is really up to the individual, and you can spin this many different ways, but we should be fair about it.
Water by and large from aquariums as stated above... is not a large factor.
Cost or ecological and when the larger issues are entirely ignored.... sort of ironic at the end of the day.