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How To Do Water Changes For Freshwater Tanks

Updated on November 4, 2007
If scientists need to do water changes for their fish, so do you.
If scientists need to do water changes for their fish, so do you.

Weekly water changes are vital to the health and well being of any and all wet pets you have. Unlike in their natural homes, wastes and bad chemicals don't float away from the fish's home. The sides of the tank prevent that from happening. You have to remove or dilute the bad chemicals for them. You don't need to remove all of the water every time. Usually, you only need to do a partial water change for freshwater pet fish like goldfish or freshwater tropical fish.

You Might Need To Change The Water More Than Once A Week

Hopefully, you haven't overcrowded your tank and have bought the biggest tank you can afford, giving at least two gallons per one inch of fish (minus the tail). If you have five common goldfish in a twenty gallon tank, then weekly partial water changes of a quarter or less of the water is suffucuent to keep the fish happy and not stressed. But if you have two goldfish in a one gallon bowl, you'll have to do partial water changes every day, and even that might not be enough.

Although doing partial water changes will dilute the bad chemicals in the water than can get the fish sick, you still need to leave a good bit of the water in there. They still need the family of good bacterial that the tank has developed over time. Doing complete water changes will shock the fish and be just as harmful as doing no changes at all.

If the water smells bad, looks really yellow or green, even if a week hasn't passed, the water needs changing!

And yes, even if you have the latest in filters, you still need to do partial water changes weekly. Once you get in the habit, it will only take up a few minutes per tank of your week.


What you need for a successful and smooth water change is:

  • One bucket only used for fishkeeping (two preferably)
  • Thick air hose or siphon hose
  • water -- at room temperature (cold water from the tap will shock and stress the fish, leaving them more suseptable to illness)
  • dechlorinator of water treatment chemicals (if necessary) Know what chemicals are in your tap water. Water testing kits are inexpensive and easy to use. Bottled drinking water is a bad substitute.

My Routine

The night before the water change, I mostly fill a bucket with cold tap water. I only fill it so I can still pick the bucket up. If you can let the water sit for 24 hours, it should dechloriate on it's own, but I can never wait that long.

For the water change, I lay newspaper down under a second bucket that will catch the dirty water. I then place one end of the siphon hose in the tank. People have different methods for getting the water going in through the hose, but what I have found to work best is sucking on the other end of the pipe. Immediately spit out any water if it reaches your mouth. If you have been doing routine partial water changes, you won't have to worry too much about getting the water in your mouth in the first place.

When the water climbs towards my mouth, I quick place the hose into the bucket and collect the dirty water. I only take out a bucket's worth for my twenty gallon. You might need more or less for your water change.

I then remove the hose, dump the water and then get a hold of the clean standing water in the other bucket. That water gets gently poured into the tank. You can also use an air hose to place the water in the tank, but I prefer just pouring the water in.

I then place Cycle in the filter system and the water change is all done for another week.

Discus getting new water and food. Film by Kubamajer


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  • flutterbug77 profile image

    flutterbug77 8 years ago from USA

    Good advice. Even though I've been keeping fish for awhile, it's always good to try and learn more.

  • profile image

    The Goldfish Guy 8 years ago

    Excellent info! If people keep up with regular maintenance of their fish tank, they should have great in keeping care of fish. Like you said water changes are vital to the survival and health of fish.

    Great article!


    Jamie BoyleThe Goldfish Guy

  • Web Gazelle profile image

    Web Gazelle 8 years ago from USA

    Lots of good information here, thanks.

  • profile image

    Don't Knock 7 years ago

    Good advice but don't knock on the glass like that! How would you like it if I knocked on your head with a hammer?

  • profile image

    Tamarind 7 years ago

    Thanks for the info.

  • profile image

    Cameron 7 years ago

    Some useful information here, but you need a larger tank. That video clearly shows the broken 'inch per gallon' rule. Those fish have no room to swim! That's crap.

  • profile image

    Stephen 7 years ago

    Just got a 10g tank for my work. I have 3 zebra danios and things are going well. I am wondering if I am supposed to change the water while the tank is cycling? Taking out ammonia will only make it take longer for my bio filter to get established.

  • profile image

    Guest 6 years ago

    It's a QUARANTINE tank. That's why it's small.

  • profile image

    Me 5 years ago

    You ALWAYS do water changes while the tank is cycling. In fact, you should do water changes every other day; it won't slow down the process.

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