Nitrate Removal in Freshwater Aquariums

Nitrate Away...

Previously, we explored the importance of cycling a new freshwater aquarium and the role of the nitrogen cycle in harmful waste removal. Unfortunately within freshwater aquarium systems, the bacteria of the nitrogen cycle can assist us only so far with nitrogenous waste elimination. Once nitrogenous waste has been converted into nitrate, alternative means other than bacteria must be utilized to completely remove nitrate from the aquarium. In this article, we will focus on different methods in which freshwater aquarists can carry out nitrate removal from their system.

Option 1: Water Changes
The first and the most common method to get rid of nitrates is to change the water of your aquarium. Water changes consist of removing a certain percentage of your aquarium water and replacing it with new water either from your tap or RO/DI system. In removing a percentage of the water from the aquarium and adding new water, you dilute the amount of nitrates found within the aquarium as seen below:

For our 150 gallon discus tank, our fish tend to produce enough waste for our nitrate levels to raise roughly 15 - 20 ppm per week. As a result we try to conduct a 70 to 80 percent water change to keep our levels as low as we can. However, even following this regimen our numbers will slowly creep higher over time. Review the scenario below. For simplicity, we work with the assumption that our fish produce 15 ppm nitrates weekly and we conduct an 80% water change once a week.

You can see that by the end of the month, the initial nitrate levels before water changes will steadily rise over time. It is important to keep nitrate levels below 20 ppm as prolonged exposure to higher levels is harmful to fish. While this scenario does not account for fluctuations with nitrate levels or alterations to the amount of water changed, you can see overall there is a positive trend. Therefore every month, we will do two large water changes in one week in order to lower our nitrate levels closer to zero.

Option 2: Plants 
Another beneficial means of removing nitrate from our aquariums is through live plants. Not only do live plants have an aesthetic appeal for aquaria, plants readily remove nitrate. As plants grow, they depend upon nitrogen which they gain through extracting nitrates from the aquarium water column. However, it is important to note that certain aquatic plants have specific light and nutrient requirements. Many planted aquariums have their own specialized light, equipment and nutrient dosing schedule for optimal plant growth. Additionally, plants will require maintenance such as pruning to prevent overgrowth and could come along with pests (such as snails). If you choose to have plants within your aquarium, this does not negate the need for water changes. Water changes also have additional benefits such as returning depleted nutrients to your system.

​Option 3: Chemical Media
Several products exist on the market which will work towards extracting nitrogenous waste. Chemical filtration is frequently stored within filters to assist with water quality. We house Seachem Purigen within our two Fluval FX6s which filtrate our discus aquarium. Purigen is a synthetic absorbent that works to control ammonia, nitrites and nitrates by removing nitrogenous organic waste. As Purigen exhausts it darkens; however, Purigen can be renewed utilizing bleach. 

Option 4: Nitrate Filter
The final way to remove nitrates is to set up a specialized filter which will create an anaerobic environment suitable for bacteria that require nitrate for survival. These bacteria will uptake nitrate from the aquarium and convert it into nitrogen gas which will escape the aquarium. This method is not commonly seen within many aquariums due potentially to the dangerous risk for fish if it is implemented incorrectly. The anaerobic bacteria must be provided with a source of carbon. Typically alcohol is used for this purpose. If too much alcohol is added to the system, the bacteria can overpopulate resulting in depleted oxygen levels in your aquarium which could prove deadly to fish. Along with this risk, there is the hassle of having to feed the bacteria with a carbon source daily. That being said, there are various versions of freshwater nitrate filters on the market which we hope to explore in the future. 

Nitrate levels are a concern of every freshwater aquarists. It should be noted, the rate at which nitrate is generated within your system will depend upon the fish you keep, stocking level and environmental factors (ex:plants). We believe the best solution for nitrate removal is water changes. Ideally, water changes should be conducted on any system to keep nitrate levels below 20 ppm. Systems with fish that produce large amounts of waste (discus) or aquariums requiring overstocked systems (cichlid tanks) will need more frequent and larger water changes compared to standard freshwater aquariums. The best way to determine your own water change needs is to acquire a water testing kit for nitrate and conduct water changes when nitrate levels near 20 ppm. We use API for nitrate testing in our aquariums.  

That's all for this installment. Keep Krill'in!