How often should I change the water in my aquarium ?

Water is essential to life. But water can also turn sour. In aquarium keeping we change the water to keep our fish happy and healthy !

Hear from Canada Aquaria members on how they manage and emphasize water changes. Why do water changes ? What kind of water conditioners do I use ? Do fish really benefit from water changes ? Why do I need to be concerned about chlorine or my local water quality ?

I change 25-30% of the water every week. I find that if I go any longer, I see a drop in the vitality of the fish, a slowdown in the growth of young fish and an increase in unwanted algae.
I'm of the generation that was taught to never change water. The balanced aquarium theory made old water precious, and told us we could balance our tiny, closed bodies of water. I wish I'd spent five minutes thinking about the stream that rushed by my neighbourhood, but we didn't look to nature for the natural aquarium. Every tank was a stagnant swamp habitat, and very few of our fish come from such homes.
When I decided to try routine water changing, many of my fish doubled their lifepan, and seemed to have healthier, more colourful lives. I stopped buying fungus medications, and a number of common fish illnesses suddenly stopped being common. I was suddenly breeding fish I had never thought I'd be able to see young from.
I'm basing this on watching my fish with what I think is a trained eye. I confess, I never use a test kit, as I should to supplement my eye. I don't care about chlorine, and as heretical as this sounds, don't see it as a problem (chloramines, however, are a deadly problem if your municipality uses them and you don't treat for it).
I never top up tanks. When the level drops, do a water change.
This hobby isn't work, so if we give our tanks a little more attention, it won't kill us. But if we neglect water changes, we may kill our fish.

The questions are appropriate for me right now, as I had to go away last weekend, missing my usual Sunday morning clean-up. My tank maintenance was already late - then I developed a couple of ear infections and was sick as a dog all week. My tanks were 16 days without a change when I got things done this afternoon - the longest I have gone in years. The result? I am treating some tail fungus in one tank, and my tanks were seriously ugly by the time I got to them. I quadrupled the work I had to do to clean up - and I hope not to do that again.

We also change 25-30% in each tank per week. We always do it on the same day at the same time: Sunday at 3pm. This way, it has become routine and a part of our schedule. Both the 5.5g and 3g, however, are changed twice a week, just to be safe where they are so small, with 25-30% taken out of the 5.5g each time, and about 45-50% taken out of the 3g (our little 'pest snail' tank!) each time

Likewise, for all the reasons Gary states. My white clouds school and dance after a water change, and usualy spawn, too.

I do 50% for the bristlenoses and like shell, I do big water changes on my pest snail grow-ops, often 75%.

The planted shrimp tanks don't require changes as often, I do them every few weeks.

For the fish I keep, large South/Central American cichlids, clean water is a major factor in keeping them healthy. You cant do too much w/c for such fish. Mine get at least 100% weekly. For most aquarists, monitoring water parameters will indicate how often a change is needed. Ammonia or nitrite spikes, nitrate readings of over 20ppm say its w/c time.

I change 50% once a week around the same time on Sunday's

When I used to keep discus, I enjoyed growing out juveniles.  For me, that meant 70% daily water changes in a 75gallon tank.  My goal was to grow them out as big and as fast as possible because their window of growth is small - about a year.  I heated and aged the water and the parameters were pretty close to the tank water so that meant less stress to the fish.  Multiple daily feedings produce waste and I find that fish grows faster and are less likely to contract diseases with clean water.

These days, I let the tank tells me how much water to change.  High nitrate producing tanks, may need 2 x 50% water changes a week.  Canister filtered tanks in fully stocked tanks produce the most amount of nitrates.  Most other tanks are 50% weekly.  

Sometimes several partial water changes during the week to held induce spawning.

I use a water conditioner to remove traces of chlorine and heavy metals in our water supply.

I like doing weekly 25% changes, if I have extra time during the week, I'll do a second change. At the maximum, I'll go 10 days.

I'm curious if people also vacuum the substrate with each water change, or if vacuuming is only done once or twice a month, for example? Over Christmas we did a few strict water changes, without vacuuming, as we were pressed for time (it was quicker to just suction cup the hose in there and pull some water out!), but we generally do a good weekly vacuum with each water change. Is the norm for others?

I always vacuum the substrate when I do a water change, some times more thoroughly than other times.

I do about a 30% water change on each tank once per week. Since the palu has very little surface agitation, it sometimes gets a few "manual skims" partway through the week which involves removing and replacing about a gallon of surface water.

No vacuuming here as I have heavily planted tank and the eco complete substrate breaks down everything to be fed to the plants. But I do 25% weekly water changes 

Shell wrote:I'm curious if people also vacuum the substrate with each water change, or if vacuuming is only done once or twice a month, for example? Over Christmas we did a few strict water changes, without vacuuming, as we were pressed for time (it was quicker to just suction cup the hose in there and pull some water out!), but we generally do a good weekly vacuum with each water change. Is the norm for others?  

I use a gravity siphon method with fairly narrow hoses (not the horrid water wasting python:-) emptying into a bucket so essentialy I remove water in the process of vacuuming. Works well with sand substrate, planted tanks etc. It allows me to selectively remove mulm and snails without snagging fry or shrimplettes.
My small shrimp tanks get vacuumed every couple of months, other tanks with heavier bioload are done weekly.

On Grow out discus I change anywhere from 75 to 100% a day. Adults I change 50 to 75% every other day. All my tanks are bare bottom so they also get a wipe down on every water change. I only use Aqua Clears or sumps. The foam in the AC get squeezed out in a bucket every week or less. I alter sponge squeezing as I run two foams in every AC. My sump gets cleaned once a week.

I use water mixing barrels that are aerated and heated,no chemicals used as we just have chlorine to deal with. Been doing this for 10+ years and it works great.