How to Lower Nitrate in Freshwater & Saltwater Aquarium

Most aquarium owners understand the dangers of elevated ammonia and nitrites in an aquarium.

But the effects of nitrates might be overlooked, especially if all the other levels in the water are within safe range.

The truth is, high nitrate levels can cause a lot of problems in your aquarium over time. It’s important to take care of any problems as soon as they’re discovered.

How Nitrate Levels Affect Aquarium Fish?

To understand how nitrate affects fish, let’s take a look at what nitrate is and where it comes from. The most significant waste in an aquarium is ammonia, which some from leftover food, fish waste, or dead plants. As ammonia cycles through your filter and comes in contact with the beneficial bacterial colonies, it is turned into nitrite and then broken down further into nitrate.

While ammonia and nitrite can be deadly to fish, nitrate is broken down so much that you might assume it won’t have much effect. The problem is that if it’s allowed to continue to accumulate, it will eventually cause problems for the fish.

What happens to fish? When the nitrate gets too high, it causes a lot of stress to the fish, making them more susceptible to disease. It can also cause problems with reproduction and is particularly harmful to young fish. It can stall their growth and development. That’s not all, it can also affect the oxygen levels in the tank which adds even more stress.

As nitrate levels increase, the problems become more serious. Fish start to get lethargic and may develop open sores or red spots on their skin. One of the scariest ways nitrate affects fish is by causing sudden death, especially in newly added fish that haven’t had time to acclimate to the slowly rising nitrate.

What Level of Nitrate in Aquarium is Safe?

Typically, nitrate will have to reach levels of 100 ppm to cause harm to fish but that doesn’t mean that you should leave nitrates go if they’re less than that.

Ideally, nitrate levels should be less than 5 to 10 ppm. Once you start getting levels of 20 to 50 ppm, it’s time to start treating the water. Remember, the threat of nitrate is that it isn’t harmful until it builds up so, to effectively prevent any problems, you have to deal with it before the levels get too high.

How to Test Nitrate in Aquarium?

The best way to test for nitrate in an aquarium is to get a kit that’s designed especially for that purpose, like this API test kit. This is a little different than the typical dip sticks you use for weekly testing.

First, use a clean test tube and add 5 ml of water. Use bottle #1 and add 10 drops to the test tube. Place the cap on the tube and invert it back and forth a few times to make sure it’s adequately mixed.  Take bottle #2 and shake it vigorously for about 30 seconds. This is really important for accurate results.

Next, add 10 drops of bottle #2 to the test tube. Cap the tube and shake vigorously for a full minute. Then wait 5 minutes for the color to completely develop. Match the final color to the color card, being sure to look at the correct one for freshwater or saltwater.

How to Lower Nitrate in Aquarium?

One of the first things to do to lower nitrate in an aquarium is to try to understand why it was too high in the first place. Overfeeding, overstocking, dirty filters, and dead and decaying plants are all major culprits for raising nitrate.

Basically, anything that speeds up the accumulation of waste will eventually cause problems. This is true whether the tank is freshwater or saltwater. That said, lowering nitrate is a little different in each kind of tank.

Lower Nitrate in Freshwater Aquarium

So, what can you do to lower nitrate in a freshwater tank?

The easiest way to quickly solve the problem is to do a partial water change. It important to only change 10 to 20% of the water at a time. This slowly decreases the nitrates and is much easier for fish to tolerate.

Remember, it can be just as much a shock for a fish to go from high nitrates to clean water. Make the transition slowly so as not to add any undue stress.

After you do a partial water change, it’s important to address what cause the problem in the first place. Be very careful not to overfeed or overstock your tank and keep a close eye on any water plants.

Another thing you can try is using nitrate-absorbing filter media that can remove the nitrate particles from the water. And make sure you continue doing partial water changes. You should do this at least once a week.

Another thing that might help is adding live plants to the aquarium. Plants naturally keep nitrates in check and add another level to your defense.

To take care of the problem quickly, there are chemicals available that you can add to your tank to quickly eliminate high levels of nitrate. These are great for emergency situations when you have to get things under control quickly but it’s important to understand that this isn’t a long-term fix. The most important thing is to treat the cause of the nitrate because, if you don’t, the problem will just keep happening.

Lower Nitrate in Saltwater Aquarium

Saltwater tanks get high nitrate levels just like freshwater tanks – from rotting food, decaying plants, and waste. While very low levels of nitrate don’t cause many problems, it’s especially important that the level in a saltwater tank be as low as possible, especially in a reef tank. The high end of the range for a saltwater tank is 40 ppm. In a reef tank with living invertebrates, it’s 5 ppm.

You can use the same testing kit for saltwater aquariums as you can do for freshwater. The method is exactly the same. Make sure to shake the solutions vigorously as instructed and, after the color developed, make sure to use the correct card to read the results. The color-coded results don’t vary a lot between the two, but they do vary so make sure you’re getting the right results.

If you get a high level when you test, there are a few things you can do to correct the problem. First, make large water changes more frequently and change out about 20-40% of the water. Use filtered water to mix the saltwater for water changes because it’s very important the water you’re replacing with also does not contain nitrates.

As we mentioned, watch the bioload. Overstocking can put too much waste into the water. It can also quickly lead to overfeeding. Try frequently smaller feedings instead of larger ones. Watch the frozen food, too, and use a strainer when necessary to remove the liquid juices that can add pollutants to your tank.

For quick treatment, there are chemicals available that can instant reduce the nitrate in your tank. If you go this route, keep in mind that this isn’t going to solve the problem of where the nitrate is coming from so it’s only a short-term fix.