A well set up fish tank should require only filter changing. Cleaning might occur twice a year.

I would say once a week.

When the water is not clear, and you are unable to see fish, please clean your tank.

When you start hearing thos funny noise it makes when the fish swims into the side of the tank.

When the water is so green that you can't see the fish anymore!

I guess as often as it gets dirty.

Never...I don't have fish

Source: OceanBasket.com

It all depends on your tank setup. If you have no filter, the once a week. If you have a proper filter system and plant life, with algae eaters - once a year. So it all depends.

Depends on the size of the tank, number of fish, type of fish, size and type of filter, water quality etc. Check if the feeshies are smiling or not :}

A Hungry Fish is a Happy Fish! Don't overfeed your fish - and the tank will stay clean much longer!

It is required to only change about 25% of your water at least every two weeks. This will prevent your fish from dying if you do not clean it often. ALTHOUGH, your fish adapt to the water PH and temperature, so cleaning out all the water once a month will eventially see all your fish dying. Rather just change 25% of the water and if you want to clean out the whole tank, then make sure you keep half of the water to put back into the tank. Remember, it is not your water that is durty, it is the algy in the tank that makes it look durty.

Kept out of direct sunlight (cos sunlight promotes algae growth), I used to work on a scrub of the glass and vacuum of the gravel, plus a one-third water change, every three to four weeks.

That would depend on various contributing factors. But in general you should clean the tank once the chemical levels become unstable aka can not sustain healthy living conditions for the fish/plant.

Depending on the size of the tank, it is advisable to vacuum the bottom (yes really) once a week. Then drain about 25% of the water and replace it with new water (treated with anti-chlorine and a pinch of aquarium salt). Remember the food and waste in the tank decompose to form harmfull nitrates and ammonia that causes disease or fish deaths. The fish tank is a closed biological system, what goes in does not come out except on the filter, and the water you drain. Do not drain all the water as a new biological system will then have to form. Good bacteria forms on the filter cloth, so when you clean the filter, wash it in the water you have drained from the tank. This will ensure that chlorine in tap water does not kill the good bacteria. The good bacteria acts the same way as the human body, it attacks and kills harmfull bacteria. By doing this you can keep the tank clean. PS! And you can always see the fish :-)

there should be a 30% water change every week and a whole tank clean less than every 2 weeks

Clean the tank twice a year. Remember to keep tank out of direct sunlight and in areas where there is lots of bright light. (Light encourages algae growth). Rinse out filters once a month with cool water. You dont want to destroy the good bacterial that live in the filters as this keeps your fish healthy and happy.

Once a week

Water changes: weekly Filter maintenance: bi-weekly Full set of water tests: monthly

I would just like to say "my fish thank you". I was going to make a quirky remark about not being able to see them... but then realised I cant see MY fish in their tank.. so they had a good cleaning out this weekend and its all sparkly and clean and the fish are ULTRA happy. It was hard work.. but worth it!

As soon as there's some algae build-up.You can also get some algae-eater fish to keep the tank a bit cleaner.