I have spent over 40 years caring for and breeding tropical fish. Over 30 tanks breeding Angel Fish, Tiger Barbs, Discus, and others.
How to Change Water in Fish Tank
It is actually not hard to maintain a happy and healthy freshwater aquarium, but it does take some weekly maintenance to keep the chemistry in balance and the quality of the water high.
Once you have an established aquarium with fish, plants, rocks, decorations, filters, and aeration, then you need to keep the water quality where it has to be to maintain life in your aquarium. Obviously, mechanical filtration is a must, but many don't realize that the water quality will become quite poor as the fishes' waste and decayed food (which becomes ammonia) will increase the build-up of nitrate (NO3), a harmful chemical that will build up to lethal levels if left unchecked.
In addition, the waste will become food for certain types of bothersome algae in your tank, and that will diminish the amount of oxygen in the water. The water will basically become polluted, unless you are prepared to do regular water changes.
Cleaning My 55-Gallon Fish Tank
Think of a water change like you would imagine a hard rain in the Amazon or a flowing river always bringing in fresh, clean water. A water change is no different, and I personally do one each week. I have a 55-gallon aquarium with six very large angel fish, two large Silver Dollar fish, and about 15 smaller fish like tetras, catfish, and barbs.
Because I feed my fish frozen food every day, either blood worms or brine shrimp, I have to be careful and not miss a weekly water change or the tank will be put under stress.
Even if you have a smaller aquarium, 10 gallons or less, you have to be alert to the water quality and not only the filtration of solid matter or gases in the water. Filtration will not help you keep your pH in check or the water hardness or other chemistry.
Schedule Your Weekly Maintenance
Determine one day each week that you will perform your maintenance. I like to do mine on a Friday so I can enjoy looking at my nice clean tank on the weekends. I use the plastic buckets I bought at Home Depot or Lowe's for around $3.50 each. I use one for the water only and the other for the plants and rocks I clean.
Simple or Complete Changes?
Please note that I do a complete water change because I have artificial (plastic) plants in my tank that get full of algae. If you have live plants, you only need to do the simple water changes, every week. You may have to remove some of your live plants and gently clean them in the sink, but this is usually something you won't want to do for fear of disturbing the roots, etc.
I use to have live plants, but after trying to fight black algae in my tank, I gave up and went to plastic plants that I can clean easily.
Step-By-Step Instructions for Simple and Complete Changes
There are two sets of instructions below.
You will see the letter A for the simple water change instructions and the letter B for the complete water change. I hope it is not too confusing.
1-A. Simple Change: Prepare the Tank
I am only going to clean the glass in the tank and remove the algae. I then take off the glass cover of the tank and use my gravel vacuum to remove 20–30% of the water with gravel sediment.
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1-B. Complete Change: Prepare the Tank
On a complete water change, I will clean my glass as above and then remove all plants, rocks and accessories that have algae on them and put them in one of my empty buckets.
2-A. Simple Change: Remove 15 Gallons of Water
I will remove about 15 gallons from my 55-gallon tank. I will either use the water I remove for my flowers and plants, in and outside of my home—after all, it is like liquid fertilizer now. Thinking green is a good thing. If you don't want to bother, simply pour it in your toilet.
2-B. Complete Change: Vacuum the Aquarium Floor
In a complete water change, you will have better access to the entire aquarium floor, so you will carefully vacuum the entire area, you will see all the sediment being removed as it goes up the tube on the vacuum. I do this until it begins to run clear and I have covered the entire floor of the tank.
3-A. Simple Change: Replace the Water
I now begin to put the water back into the tank, making sure the water temperature is about the same as what it is in the tank. I do this by feel and my experience, but if you are not sure, use a thermometer to make sure the water is not too cold or too hot.
See my photo to see the proper way to pour the water back. I use my hand to break the force of the water and spread it out so I won't disrupt the gravel or plants in replacing the water.
4-A. Simple Change: Put the Top Back on, and You're Done!
Once the water is back in the tank, you can replace the glass top and you are good for another week.
3-B. Complete Change: Soak the Rocks and Plastic Plants in a Bleach Solution
In my complete water change, I will do the same, but we need to clean our rocks and plastic plants in a solution of 1 part Bleach to about 30 parts of water. I actually pour about one cup of bleach in a 5-gallon pail that is filled with my plastic plants, rocks, air stones, tubing, etc. Once I have the bleach in, I add hot water to fill the container and let it stand for about 15 minutes or until the algae is gone from the rocks and plants.
4-B. Complete Change: Repeatedly Rinse the Accessories to Remove the Bleach
Since they have been soaking in the bucket (I do this in my bathtub) after my 15–20 minutes, I will remove the bucket and pour the water/bleach solution into the toilet and hold my hand on the plants and rocks. I do this slowly so nothing gets poured into the toilet by accident. I had a plastic plant go down the toilet so fast, that I couldn't catch it. Fortunately, it was a soft plant and went right down. But be careful. I often take out the heavy rocks and wash those in clear water separately. You can of course dump the water in the bathtub, but then you have to wait for it to go down the drain to refill the bucket.
Now fill the bucket another 4–5 times, swish the plants with your hands a few times to help remove any of the bleach and dispose of the water.
Warning: If you don't completely remove all the bleach from your plants and rocks, you can kill all the fish in your tank. So be sure you wash everything in clear water completely.
5-B. Complete Change: Scrub the Accessories (Optional)
If you want to clean the rocks and accessories better, you can do this in your sink. I put in a heavy hand towel in the sink to prevent any scratching or damage to the sink from the rocks. I use a small fingernail brush to scrub the rocks and accessories.
6-B. Complete Change: Replace the Accessories and the Water
Take the clean plants and rocks and replace them in your aquarium. You may find it easier to do this before you replace the water on a complete change.
Now you have the plants, rocks and accessories where you want them, then you can add the water (just like we did in steps 2-A and 3-A for the simple change).
Before and After
7. Clean the Filters (One Day Later)
Some people like to change or clean their filters with fresh filter materials and charcoal every two weeks, so you can do this after a complete change if you like.
One suggestion is to wait one day on the filter change. After you do your water change. Let the filter clear out any floating material in the tank that is now floating in the water and then do the filter change.
8. You're Done!
That's it. You just did what nature did with one of those hard thunderstorms in the Amazon River. You have flushed away all the waste material in the tank, you have diluted any of the harmful chemicals and put your system back in harmony.
Tips and Advice on Easy Tank Maintenance
- Don't be too concerned about the amount of chlorine in the replacement water, I will use a little of the chlorine remover sold in pet shops, but frankly, it should not really be a problem since you are only replacing about 20% of the water.
- I like to put a little salt in the water. I use about 1 tablespoon per 15 gallons of water. Kosher or Aquarium salt serves as a general tonic and stress reducer for freshwater fish. I have used it for years. Do not add salt if you are simply adding water that has evaporated from your aquarium, the salt hasn't.
- If you are adding a lot of water in a big tank, you may want to use the chlorine remover in the water; small water changes don't really need to do this.
Why Changing the Aquarium Water Matters
Your fish will get used to your water changes as they get used to you feeding them each day. They will not get stressed out and will feel better once it has been done. You will see them come alive after a change and in some species, this is how you entice them to breed.
If you fail to do water changes regularly, the poor water quality can lead to infection in any wounded fish. It will also put stress on fish, which is often the cause of fungus and parasite issues.
© 2009 Len Rapoport
Megan Nelson from Spokane on April 11, 2018:
It's nice to see another aquarium hobbyist who keeps up on their water changes. I work at a fish shop and I try to stress to all of my customers of how important weekly water changes are. Your article was a great read and a joy to discover!
Rain on November 02, 2016:
Just wondering how much to feed my fish I have 4 - 2 neons, one little cat fish, and one other small fish about 1 inch long???? My tank is only 10 gallons - a larger tank is to heavy for me to take apart and clean etc - I've had it for two years and it's been pretty nice, but my daughter thinks I feed them too much.
podger78 on October 25, 2016:
Awesome re clean your tank then when adding back water let the filter work then change the clean the filter next day thanks
Tiru on September 05, 2016:
I changed the water and used bleached water without knowing. Now the fishes are becoming weak and dull. What to do to protect them? Plz suggest.
Len Rapoport (author) from New Jersey on September 29, 2012:
It depends on your fish in the tank. Generally the temperature for many fish should be between 75-85 degrees. Check with your local pet shop or do some research on the web based on the fish you have.
simon on September 08, 2012:
Wot temp do I need to maytan in my tropical tank plz I need help
dbialecki on April 10, 2012:
This is a nice detailed guide regarding water changing. I've seen so many hobbyists not change it often enough and it really is a shame. Bravo!
Len Rapoport (author) from New Jersey on October 15, 2009:
Yes this is my only remaining tank. At one time I have 30 tanks, most in my basement and I was breeding fish for sale to local pet shops. Of course now they are all chains and they buy sick fish for pennies and sell them for big bucks. When I was breeding the fish, mine were healthy, raised by hand and not in large vats and ponds and they were huge in size when I sold them.
Darlene Sabella from Hello, my name is Toast and Jam, I live in the forest with my dog named Sam ... on October 07, 2009:
I love this article Len, is this your own fish tank? Did you take these pictures yourself? Very cool article, WTG