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How Much Does it Cost to Maintain a Freshwater Aquarium?

High-tech planted tank

Freshwater aquariums can run the gamut from simple, low-tech, 10 gallon tanks with a betta, filter, and a heater, all the way to 1,000 gallon systems with hundreds of fish and plants, sumps, electronic controllers, app-enabled lighting, and CO2 gas injection.

Regardless of which system you have, or plan to build, the formula for calculating how much maintenance will cost you is the same. The only difference is the cost of each variable or component in the formula.

The Components of Freshwater Tank Maintenance

Aquarium maintenance occurs on a daily, weekly, and monthly basis. The associated costs build with each action. Calculating how much it will cost to maintain your aquarium is simply a matter of adding together the components for your system.

The components of freshwater aquarium maintenance are water, additives, filter media, carbon, water analysis, food, and new livestock.


For freshwater aquariums, water is not the most expensive component, but it is the basis on which many other components are built. Whether you use tap or premixed vs. self-mixed reverse osmosis deionized (RODI) water will determine how many additional additives you will use with every water change.


Tap water is different all over the world. Some is fairly pure, some is laden with heavy and toxic chemicals. Using tap water is the least expensive source for water changes. After looking at your local municipality’s water report, and determining if your tap water has the correct parameters for your tank, you can expect to spend as low as $.005 per gallon.

RODI Water at Home

If your tap water is not suitable for aquarium use (most isn’t) you can install an RODI filter in your home and make your own reverse osmosis deionized water. This article gives a quick introduction to RODI filters. Once you’ve installed an RODI filter, you can start making your own pure water for as little as $.15 per gallon.

RODI Water From the Store.

If your aquarium is small enough and installing your own RODI filter is more than you need, most aquarium stores will sell RODI water. At retail, RODI water will cost you at least $.50 a gallon.


Additives are chemicals added to water in order to change its chemistry. The first additives used alter the general and carbonate hardness of the source water to match it to the aquarium water. Optional additives include fertilizers, water conditioners, algaecide, medication, and correctives. Which additives are used depends on the source water and types of filtration.

General and Carbonate Hardness

The additives that raise and lower general and carbonate hardness are always necessary when using RODI water and sometimes tap water as a source. This article details the appropriate levels of GH and KH for different types of freshwater.

Depending on the brand of GH and KH additives you use, or whether you use liquid, powder, or buy in bulk, the cost for these additives will cost you at most $.045 per gallon.


Planted freshwater tanks require fertilizers. These can be one of the most expensive recurring parts of aquarium maintenance if you have a high-tech planted tank. A heavily planted aquarium with CO2 gas and high lighting is considered high-tech. Fertilizers for high-tech tanks can cost upwards of $.037 per gallon per week.

The other end of the spectrum is a low-tech planted tank with no CO2 and low lighting. These tanks require less fertilization and can cost as little as $.004 per gallon per week.

Other additives

If you're using tap water, a de-chlorinator will be your most frequent expense for additives at $.014 per gallon. Other chemical additives like bacteria, aquarium salt, and phosphate and nitrate removers will be a little pricier at nearly $.10 per gallon, but are less frequently used.

Medication is the most expensive single additive at around $.20 per gallon. However, these are rarely used when systems are maintained appropriately.

Filter Media

Like with most things, an ounce of prevention is with a pound of cure. Filter media can quickly become an expensive part of your maintenance if you have to keep replacing filter pads, costly chemical adsorbing resins, and refiling reactors every few weeks.

With Freshwater aquariums, there are ways to reduce the cost of filter media. Using live plants and creating a healthy aerobic and anaerobic habitat for beneficial bacteria is a great start.

Physical Media

Depending on your bioload, filtration media will need to be replaced on a regular schedule. This article details how often to clean an aquarium. Depending on the filter type, tank size, and bioload, new socks, pads, or sponges for physical filtration can cost as much as $.04 per gallon or as little as $.02. The average per gallon is $.03.

Chemical Media

Activated carbon and ammonia, phosphate, and nitrate adsorbers are forms of chemical filtration. As they adsorb their respective nutrients and chemicals they will need to be replaced. Depending on the bioload of your tank, expect to spend, on average, $.04 per gallon for carbon and between $.20 and $.07 per gallon for nutrient adsorbers, with $.13 being the average.

Biological Media

The main type of biological filter media is a habitat in which beneficial bacteria live and reproduce. This media type should never be replaced and therefore has no maintenance cost.

Biological media can also include periodically adding live bacteria, the cost of these supplements is about $.01 per gallon.


There are several ways to add carbon to your tank for plant growth. The first is by adding a liquid carbon supplement. This will cost about $.01 per gallon per week.

While liquid carbon supplements are inexpensive, an even more cost effective and efficient form of carbon injection is using a regulator and gas cylinder to add CO2 gas. This article outlines the details for setting up CO2 gas on your tank. After the initial investment, CO2 gas costs as little as $.0056 per gallon per week.

Water Analysis

At Home

If you're testing at home, using color changing liquid reagents, handheld colorimeters, or titration tests, you can expect to spend around $.10 per test. With around 6 tests per week, that is $.60 per week in testing.

At The Store

Most pet stores will not charge for water analysis if you're a regular customer. I have seen some stores charge up to $2.00 per test when using higher grade testing equipment.


For most freshwater aquariums, feeding dry food every other day, and frozen food thrice weekly, costs about $.014 per gallon per week. If your aquarium is heavily stocked, or if you're feeding large fish with specialty diets, expect to spend closer to $.035 per gallon per week.

New Livestock

While I don’t consider this maintenance per say, a recurring cost for most freshwater aquariums is new livestock. This amount is relative and could be as little as a few dollars a year for established aquariums or up to hundreds of dollars a month for new aquariums. I won’t include this in the final calculation, but consider how much adding livestock will cost you.

So How Much is The Cost of a Freshwater Aquarium?


Per gallon ($)

Per gallon/week ($)

Per Week ($)

Tap Water


RODI (home)


RODI (store)




Fertilizers High-Tech


Fertilizers Low-Tech




​Misc. Addiditives




Physical Filter Media


Activated Carbon


Nutrient adsorbers


Live Bacteria


Liquid Carbon


CO2 Gas


Water Test


Food Light Bioload


Food Heavy Bioload


Adding all our average costs together, the final total to maintain an average freshwater aquarium per gallon is $.10 per gallon per week, plus $.60 per week for testing.

Now, this is the average cost per gallon per week. This average was derived from the individual averages for each component. This total per gallon per week includes the average cost of tap, self-made, and store bought RODI water. It includes the average cost of a heavy and light bioload.

For your specific setup, use the table above and add up your relevant costs per gallon then multiply by your tank size, or water change volume.

When doing your own calculations, each total is per gallon. However, if you do water changes monthly, then your total will be per gallon per month, not per week. For example, the total cost of GH/KH additives with weekly water changes on a 100 gallon tank (25 gallon water change) would be $1.12 per week, or $58.24 per year. The total cost of GH/KH additives with monthly water changes on a 100 gallon tank (25 gallon water change) would be $1.12 per month, or $13.44 per year.

Keep in mind, your additive calculations will be multiplied by the volume of your water changes, not the entire tank volume. Filter media and fertilizer calculations will be multiplied by the entire system volume.

Finally, when doing your own calculations, remember, the .60 per week for water testing is not per gallon, it's per week. So the total for water testing should always be ($.60 x 52) = $31.20 per year. Add the $.60 to the end of the weekly total for your system volume, not the per gallon total.

For example, a 50 gallon tropical community tank with no plants, a light bioload, and using tap water, would cost about ($.12/gallon/week x 50 gallons) = ($6.33/50gallons/week + $.60) = $6.93 per week, $27.72 per month, or 332.64 per year.

A 120 gallon high-tech planted tank with a heavy bioload, using self-made RODI water, would cost about ($.092/gallon/week x 120 gallons) = ($11.13/week + $.60) = $11.73 per week, $46.92 per month, or $563.04 per year.

The cost per year for the 120 is higher than the 50 gallon because of the larger tank volume, but the cost per gallon is lower. This is due to the plants providing nutrient removal which reduces the cost through less frequent water changes and fewer nutrient removal chemicals and resins.

Keep in mind these are averages. Some people buy in bulk, do less frequent water changes, or only feed dry food. These can change your annual maintenance total significantly. My 38 gallon high-tech planted aquarium, with light bioload and self-made RODI water costs me around $80 a year in maintenance costs. According to the above calculator, it should cost me closer to $168.00. However my bioload is very light, I don’t change the filter media as often, and I only do monthly water changes.

Plan Ahead

I hope this article helps you calculate the cost of maintenance for your freshwater aquarium, and gives you an idea of what to expect when building your next system.

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