How to Quickly Lower High Nitrates in Your Aquarium

Sometimes it's necessary to lower the nitrate levels in your fish tank or aquarium. High nitrate accumulation, also known as old tank syndrome, is a common issue for long-time aquarium enthusiasts. It often occurs when regular maintenance and water change routines are neglected, leading nitrate poisoning in fish.

This method provides an instant reduction of nitrates through a water change. You can quickly reduce nitrate levels to zero without harming your aquarium residents. The behavior of the fish may improve as well; they might become more active, eat better, and display brighter colors in a few days.

Here's how to lower nitrates in a fish tank or aquarium without harming your fish and other tank inhabitants.

What is Nitrate?

Nitrate is the end product of bacterial reduction of ammonia to nitrite and then to nitrate. The nitrate will accumulate in the aquarium water until it is assimilated by plants or removed by water changes.

Proper Nitrate Levels

In freshwater, nitrate is relatively nontoxic even at high levels (200 mg/L or more), but in saltwater aquariums, it can be a problem for marine invertebrates, so it should be kept at lower levels (below 20 mg/L).

Some marine aquarium keepers are reluctant to perform regular water changes to lower the nitrate because they would then need to add more salt into the aquarium. Instead, they may top off the evaporated water with fresh water since salt does not evaporate. This does not remove nitrate. Instead, it allows nitrate to rise and can cause problems in the aquarium.

Before You Lower Nitrate Levels

Before you start a water change, remember that it will change the pH in your tank (probably upward). Before beginning this water change, it is wise to slowly adjust your tank water pH to where it will be when you are finished. You can adjust the pH upward with common baking soda or downward with one of the many products on the market to reduce the pH of aquarium water. This will prevent your tank critters from going through "pH shock," which can be fatal to more sensitive tank critters.

How to Lower Nitrate Quickly

Many people try to reduce their nitrate levels by performing a series of partial, 20 percent water changes. This will reduce your nitrate (or any other chemical substance) levels, but it is rather inefficient if the object is to reduce the levels to near zero in the fastest time possible, with the least amount of water.

For example, if you reduce the level of water in the tank to 20 percent of normal and then refill the tank to a 40 percent level, you have already reduced your nitrate levels by half. If you then refill the tank to the 100 percent level, your nitrate levels will be 20 percent of the original level that you started at.

If, on the other hand, you reduce the 40 percent water level once more to 20 percent and then refill the tank, you will end up with a nitrate level of 10 percent of what you started with. Perform the 40 percent to 20 percent reduction once more, and you will end up with a nitrate level of 5 percent of what you started with. So, if you started with a nitrate level of 100 parts per million and used this method, your 100 ppm nitrates would be reduced, in a short period, to five ppm, which is considered to be an acceptable level even for corals.

Safety Considerations

Some people fear that the rapid reduction of nitrate would "shock" tank critters. This is an understandable concern, but under the circumstances, the rapid reduction of potentially harmful toxins in a tank is of the utmost importance.

For example, it would be like standing in a closed garage with a car engine running, filling the garage with carbon monoxide. Then imagine someone telling you not to open the garage door since the rapid reduction in carbon monoxide levels is more harmful than reducing the carbon monoxide levels by 20%. The scenario is the same. The fish and other tank inhabitants are swimming in a toxic substance that will kill ​based on exposure.

You can be conservative while using the above method if you're concerned about "shocking" your tank inhabitants. Perform the process over time, waiting a few days between each water change, until the nitrate is reduced.

How to Prevent High Nitrate Levels

The best way to avoid the urgent need to have to reduce toxic nitrate levels is to follow a regular maintenance and water change routine. If you find you are in a position where everything you have tried does not seem to work and rising nitrate levels continue to be a problem, give this water change method a try.