Aquarium Water Changes – Freshwater

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Siphoning water out of aquarium
Siphoning Water

Aquarium water changes make the difference for healthy fish, without proper water changes and substrate vacuuming your fish will be swimming in caustic and hazardous water.  Rotting food, fish poo, or plants decomposing can cause ammonia buildup in the substrate releasing into the water column.  Water changes are the most dreaded task of owning an aquarium, but are essential for maintaining the health of your aquarium and most of all your fish.  Regular water changes will help maintain the water chemistry in your tank, if you let the ammonia build up it will be harmful to your fish, leaving you wondering what happened.

Having live plants, driftwood, alder cones, or some other natural products that are found in their natural habitat will aid in keeping water parameters within the correct levels. No matter how much natural matter is in the aquarium, water changes will always be needed.


How often should you complete an aquarium water change?  No matter where you look, you will get different answers; two times a week, once a week, every two weeks, etc.  The frequency will depend on many factors; when do you have time to do it, how many fish do you have and what size tank, do you have live plants, are you growing out fry, or do you over feed?  Many factors can determine the frequency needed; as time passes, you will figure out what is a good interval that meets time available and tank requirements.

Aquarium Water Changes with Substrate Vacuuming

Substrate vacuuming, using a gravel vacuum; it’s not required every time you do a water change but needs done on a regular interval of a month or less.  I suggest an interval of every other water change; This may be excessive if you only have a few fish in say a 29-gallon tank.  A 29-gallon tank with a few small fish, monthly gravel vacuuming will suffice, considering you are not overfeeding or a large amount of plant matter is not decomposing.  If you miss a regular scheduled substrate vacuuming, keep in mind that when substrates stirred up all that ammonia resting in the substrate will release into the water.  Releasing too much at one time can create an ammonia spike that can be fatal to your fish.  As you vacuum the gravel, you may notice small bubbles rising to the surface, that is ammonia.  To avoid this, only doing half the substrate and wait a few days before doing the other half. 

Recommended Timeframe:  Once a month with light to moderate stocking levels

Water change only

Changing just the water should be determined the same way as for vacuuming substrate; fish quantity, tank size, feeding habits, etc.  With a substrate vacuum interval of one month at a minimum every two weeks you should do a water change, every week would be better.  Water changes are imperative to keep the water chemistry level and within acceptable ranges regarding ammonia, nitrate, and nitrite. Any sudden fluctuation in those levels you should consider a water change. 

Recommended Timeframe:  Half the time of substrate vacuum, or as often as possible.

With the frequency stocking levels, size of the tank, the number of fish, plants, feeding habits, and availability to complete the water changes needs consideration to determine the adequate timeframe.

Percentage of Water Changed

The percentage of aquarium water to change will depend on tank conditions. Does your tap water need pre-treated water or just  straight from the tap.  Pre-treating water will require a storage container that is clean and has not been contaminated from anything other than water storage for your aquariums.  Pre-treating water needs to be considered prior to water change day. I suggest using Seachem Laboratories Prime, it will remove chlorine, chloramine, and ammonia.

How are you getting treated water or straight tap water to your aquarium, I am sure all aquarium hobbyists have lugged 5-gallon buckets of water.  Moving water by a bucket is easy, but if there are multiple tanks or large tanks that need filled it will become an issue and lead in inadequate water changes.  

How much water needs changed out each time?  Good rule of thumb is 50% water change every time; This will ensure a minimum of 100% water changes monthly.  Breeding fish or injuries to fish water change frequency needs to increase. Fish with disease or injury water changes once a day are needed.  In non-breeding, non-fry tanks 20-25% changes twice a week is what I prefer given I have the time to do the frequency.  Breeding and fry tanks a 40-50% water change twice a week, giving you 80-100% water change a week.

Prior to creating my fish room, I had (1) 29gal and (2) 20gal tanks that would take 2 hours to complete the water changes and cleaning equipment, my fish room I have now with 10 tanks of varying sizes and the water changing set up I have takes me just 1 hour.  If you are struggling to maintain a regular water change schedule, consider other options to complete them in an easier or less time-consuming way.

Conditioning water

Water out of the tap contains unhealthy chemicals to fish, that your local water authority uses to ensure your drinking clean water.  Determining those levels you will need to complete a water test.  Chlorine is in all water from the tap; levels will vary by location, but the EPA requires it to be at detectable levels.  If you have well water you may be lucky and will not have to worry about any added chemicals from the municipality, testing is still recommended for your water to ensure it is safe for your aquariums.  To test your water, a testing kit will run you $10-$150, while laboratory testing can run from $50-$500, if you are looking at having expensive fish this test may save your money in the long run. 

Chlorine is easy to remove, one way to do that is to just aerate your water for 24 hours this will help the chlorine evaporate off.  Tap water conditioners are another quick option that also removes other contaminants almost instantly, just remember this is also a chemical although safe for aquatic species is still a chemical.  Tap water conditioners work great if you do not have a storage container to allow tap water to evaporate all the chlorine off, it also detoxifies heavy metals in water. 

Maintaining your water quality; through adequate aquarium water changes will ensure you have healthy and happy aquatic species, remember if you are new to the hobby the best place to get information is from fellow hobbyists.  To maintain a constant water change program, it has to be something that’s not dreaded every week or 2 weeks that you do it.  If it becomes a chore, you’re not enjoying anymore consider a new system that be more enjoyable and less time consuming. 

Keep It Fresh!

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