How Much Water Conditioner Per Gallon? (Aqueon, API & Others)

Many aquarists already know that water conditioners are necessary for fish tanks since they quickly take care of ammonia, chlorine, and chloramine. However, there are many types of conditioners, and each one requires a different amount per gallon. In this article, I will teach you how much water conditioner you should put in your tank.

When using Aqueon and Tetra AquaSafe Plus, use 0.50ml of product per gallon. Seachem Prime is more concentrated and requires merely 0.10ml per gallon. Tetra Easy Balance and the API water conditioners are more diluted, which is why you should add 1.00ml and 1.67ml from those, respectively.

As we move forward, I will teach you what could happen if you add too much water conditioner and its effect on your fish. Then, I will show you how to apply the conditioner to your tank correctly and what would be the most cost-effective choice when considering different kinds of conditioners.

How Much Water Conditioner Should I Use? (For 0.7-55 Gallons)

This table describes how much water conditioner you should add, considering the number of gallons your aquarium holds and the type of product you use:

GallonsAqueon [ml]Seachem Prime [ml]Tetra AquaSafe Plus [ml]Tetra Easy Balance [ml]API [ml]

Everyone understands the benefits associated with water conditioners. They remove toxins like ammonia, chlorine, chloramine, and phosphates. They can also reduce the stress in a fish and eliminate heavy metals. In some cases, water conditioners enhance the recovery of the creature’s slime coat.

But water conditioners can only deliver those benefits and more if you apply them in the right quantities, which is where many beginners struggle. They do not know the right amount of water conditioner to add to their tanks, especially if they have multiple tanks of varying sizes.

If you have found yourself in the same boat and need a straightforward answer regarding the right amount of water conditioner to add to your tank, you might be surprised to learn that a straight answer doesn’t exist.

On the one hand, many aquarists use a ratio of 5:10 when adding water conditioners, that is to say, 5mls for every 10 gallons of water.[1] With that ratio in mind, it won’t take you long to calculate the amount of water conditioner you should add based on your tank’s size. 

For instance:

  • 0.7-Gallon Tanks require 0.35mls of water conditioner (7 drops)
  • 1-Gallon Tanks require 0.50mls of water conditioner (10 drops)
  • 1.6-Gallon Tanks require 0.80mls of water conditioner (16 drops)
  • 2-Gallon Tanks require 1.00mls of water conditioner (20 drops)
  • 2.5-Gallon Tanks require 1.25mls of water conditioner (25 drops)
  • 3-Gallon Tanks require 1.50mls of water conditioner (30 drops)
  • 3.5-Gallon Tanks require 1.75mls of water conditioner (35 drops)
  • 5-Gallon Tanks require 2.50mls of water conditioner (50 drops)
  • 10-Gallon Tanks require 5mls of water conditioner (100 drops)
  • 20-Gallon Tanks require 10mls of water conditioner (200 drops)
  • 55-Gallon Tanks require 27.50mls of water conditioner (550 drops)

As you might have guessed, the quantity of water conditioner required is proportional to the tank’s size. The bigger the tank, the greater the amount of water conditioner needed. Looking at the list above, you might be tempted to conclude that the question of water conditioner quantity isn’t complicated at all.

But that conclusion is wrong. The figures listed above are only applicable to brands like Aqueon Water Conditioner, whose instructions specify a dosage of 5mls for every ten gallons of water.[2] This is where complications arise. 

Water conditioners are not all the same. They may feature similar ingredients, and they will most likely deliver similar results (depending on the type of water conditioner), but their concentration tends to vary.[3]

For example:

  • Seachem Prime has a dosage of 5mls per 50 gallons.[4] 
  • You have to add 5mls (100 drops) of Aqueon or Tetra AquaSafe Plus to treat 10 gallons of water.[5] 
  • But you only need 1ml (20 drops) of Seachem Prime to treat the same 10 gallons of water. 
  • Tetra Easy Balance has a dosage of 5mls per 5 gallons. So you need an estimated 10mls (200 drops) to treat 10 gallons of water

As you can see, the amount of water conditioner you can add to your aquarium per gallon will depend on the size of your tank and the concentration of the water conditioner in question.

That being said, this doesn’t introduce nearly as much confusion as you expect. This is because water conditioners are typically accompanied by clear instructions regarding their dosage. Just look at their packaging. It will show you the number of drops and cups that must be added to tanks of a particular size to treat your water.

You don’t have to be perfectly accurate with your measurements. Most water conditioners are safe.[6] You lose nothing by adding more than the instructions specify. Some brands may provide units of measurement that you do not fully comprehend.

For instance, they might specify the number of cups without telling you the corresponding number of drops or milliliters. In such cases, you should contact the manufacturer. They will make all the necessary conversions on your behalf.

  • Though, it might be easier to consult one of the numerous calculators on the internet. For instance, I consistently find myself checking the API UNIVERSAL CALCULATOR

Once you insert the dosage on the water conditioner’s packaging and then specify the size of your tank, these calculators will tell you the exact amount of water conditioner to apply, not just the mL and number of drops but the corresponding ounces, cups, teaspoons, and tablespoons.

Depending on your financial strength, the dosage might play a significant role in your purchasing decisions. People think that a water conditioner’s functions are all that matters. They are not entirely wrong. You have to figure out what a water conditioner does before you buy it. 

Some conditioners remove chlorine. Others remove chlorine and chloramine. You have those that neutralize ammonia, not to mention products that can manipulate the water’s alkalinity. Some conditioners are so powerful that they can do a little bit of everything.

The more functions a water conditioner has, the more money it will cost. However, you cannot ignore the dosage. Please take a moment to determine the volume of water each mL of water conditioner can treat before you buy it.

Some water conditioners have friendly price tags, but they are expensive in the long run because you have to use many cups and drops to treat a small amount of water. Others attract financially constrained aquarists because they can treat a lot of water using the fewest drops possible.

Seachem Prime (link to Amazon) is a prominent example. You can treat 5,000 gallons of water with just 500 millimeters. That is 0.002 dollars for every gallon.[7] A water conditioner that exceeds your budget is useless because you cannot use it consistently. Check every conditioner you encounter to ensure that its dosage is compatible with your pocket.

Can I Add Too Much Conditioner to my Fish Tank?

Yes, you can add so much water conditioner that it harms your aquarium. In excessive amounts, water conditioners may lower oxygen levels due to chemical reactions. However, that occurrence is quite rare. Even in high concentrations, conditioners are more likely to remove harmful water elements.

They do not interact with any other components or additives, and neither do they affect the water chemistry.[8] It is pretty tricky to unintentionally add water conditioners in quantities so excessive that they cause harm.

Seachem Prime is a concentrated conditioner that can treat several gallons of water with just a few drops. And yet, according to the manufacturers, you can add up to 5 times the recommended amount without negatively affecting your tank.[9]

It would take several gallons of a water conditioner to harm your fish. But even beginner aquarists are unlikely to add that much conditioner to a tank. The manufacturers of these products will tell you that it is better to add too much water conditioner than too little.

But again, too much of anything is bad. In the unlikely event that an aquarist adds too much conditioner to their water, the substance will bind to the oxygen, causing an oxygen deficiency.[10] But your fish are unlikely to suffocate.

You may notice some labored breathing, but the symptom won’t last long. The water conditioner may deplete the oxygen in the aquarium, but this effect is temporary. The oxygen levels in the aquarium will recover in a few hours.

Your tank will only suffer lasting damage if it already had an oxygen deficiency because of factors like high temperatures and a high bio-load. In such an instance, an overdose of water conditioners could quickly lower the oxygen to dangerous levels. You can expect similar results in tanks that have been treated with medications that lower the oxygen. However, such situations are rare.

Water conditioners are entirely safe. It is very difficult to add so much water conditioner that it causes harm. And even when you add an overdose, the side effects should be temporary. If your fish are dying, look for underlying causes. The chances that the water conditioner is to blame are meager.

How to Measure The Necessary Amount of Water Conditioner?

You have to use water conditioners whenever you add new water to a cycled aquarium. That includes the water added during a weekly water change and the water added as a means of topping up a tank whose water level has dropped as a result of evaporation.

Some people place the new water in a container before treating it with a conditioner and then adding it to the tank. In such cases, they only add enough conditioner to treat the water in the container.

Others add the water to the tank before treating the entire aquarium. You also have those that do both. That is to say; they treat the water as it enters the tank via a hose. They slowly drip the conditioner into the new stream of water.[11]

Regardless of the method you prefer, the measuring tool matters because it will affect your accuracy. While many manufacturers encourage their consumers to use the caps that cover the conditioners, most aquarists tend to gravitate towards glass droppers. That usually involves the medical models with the Milliliter measurements engraved on their walls.

You can also use syringes. But as was mentioned above, you don’t need perfect accuracy. With cups and teaspoons, you are more likely to add more conditioner than the instructions prescribed. But unless you accidentally pour the entire bottle into the water, you don’t have to worry about harming your fish.

If you found this article useful, these may also interest you:


When using water conditioners, there are two factors you should consider. The first would be the type of conditioner you use, and the second is the number of gallons your tank features. Naturally, bigger tanks require more of your water conditioner.

If you accidentally add too much of your product, the chances that it would harm your fish are pretty low. Water conditioners are safe and usually don’t have any negative impact on aquarium fish. Yet, it is still better to use the correct amounts.



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