Everything about Nitrates in Planted Tanks

Today we are going to talk about nitrates in planted tanks. However, if you are new to this hobby, you need have to learn more about the nitrogen cycle first.

We can often hear that plants can solve the problem with the nitrates in our tanks. So, people add plants thinking that they are doing everything right. Unfortunately, after some time, they get confused because the nitrates levels in their planted tanks are still too high. Why?

That is usually because they make some fundamental mistakes. First of all, slow-growing plants will not help you much. Second, floater plants are way better for that. Third, lighting and filtrating should be adequate for the plants you have.

In this article, I will be talking about all these things in detail.

Nitrates in Nitrogen Cycle

Nitrate occurs naturally in any aquarium. Basically, every time you feed your fish, shrimp, snails, etc. they are going to produce waste in the form of ammonia.

Note: Other sources of waste found in tanks usually include uneaten food, decaying plants, decaying driftwood, and dirty filters.

In its turn, with the help of Nitrosomonas bacteria, ammonia will be transformed into nitrites and nitrites into nitrates.

The ammonia is very toxic to the livestock and nitrites are even worse than ammonia. Therefore, we need to keep them as close to zero as possible.

Nitrates are not considered very dangerous BUT only when they are in small amounts!

The results of the experiments suggest that even short-term acute exposure to nitrates can cause a general dysfunction throughout the whole fish body.

According to some other observations, high nitrates can:

• slow down the growth,
• cause significantly lower fish biomass,
• decrease survival rate,
• change the swimming behavior,
• have chronic health and welfare impacts.

Another problem is that nitrate can accumulate in the tissue!  For example, when I was researching this problem related to the shrimp keeping. I found out that nitrates accumulate in muscles, digestive gland, stomach, heart, gill, hemolymph, midgut, and eyestalk of the shrimp.

Unfortunately, about 5-10% of the total nitrate intake is converted back to nitrite by bacteria in the stomach of the shrimp. Therefore, the higher is the level of nitrates in the water, the bigger is intake.

So, can we prevent nitrates from building up in your tanks?

No, we cannot prevent nitrates from building up, it is simply not possible. However, we can control and when needed reduce them in our tanks.

How to Test Nitrates in the Tank?

You need to buy a test kit. It is absolutely not possible to check water parameters without one (including nitrates). In other words, you are pretty much flying blind and hoping for the best.

This is the reason why test kits are a must-have tool! I cannot stress enough how important this is. No doubt, it must be one of the first things you buy, if you are serious about being in this hobby.

Nowadays there are many products on the market but all of them can be divided into 2 main categories:

• Test strips.
• Liquid tests.

I always recommend using only a liquid test kit. In my experience I find that the strips are not sensitive enough, therefore, they often show an incorrect reading. However, if you do not have a choice – any test kit is better than nothing.

Personally, I prefer to use an API master kit (link to check the price on Amazon). It is a liquid test kit. It tests for ammonia, nitrite, nitrate, pH, GH, KH, etc. 

1. Take the bottle “Nitrites”. Shake it for a few seconds.
2. Then you add in 10 drops from the bottle. It will turn yellow or yellow-greenish.
3. Take the bottle “Nitrates”. Shake it for 30-40 seconds.
4. Add 10 drops from the bottle.
5. Put the cap back on the test tube and shake this tube for one minute vigorously.
6. Wait 5 minutes
7. Read the results.

Note: You need to wear gloves for safety.

Tip #1: If you have a hard time seeing the colors when testing the water, hold it against a white piece of paper.

Tip #2: Keep in mind that indoor lighting can also throw out the test colors. Especially when your lights give off an orange glow.

Ideal Nitrate Levels

However, before we decide to lower or control nitrates in our tanks, we need to know when we should do that.

Nitrate is the third stage (the last one) of the nitrogen cycle and as we already know it is toxic in high concentrations. However, it does not mean that we should test the limits of our livestock.

Fish and shrimp can survive and adapt to certain levels of the nitrates. Is it OK then?

No, it is not! In the long run, this adaptation will be at the expense of the immune system.

So, what is the safe level of nitrates you may ask?

Truth be told, everyone is likely to give you their own advice in regards to ideal nitrate levels. Why? Because it depends on your tank setup and this equation can have lots of variables (a type of the tank, how old it is, livestock, what plants you have, fertilizers, lighting, etc.).

For example:

• Shrimp tanks do not like nitrate levels above 20.
• Fish tanks also depend on the species, age, and overall health, but often levels above 50 ppm are undesirable in freshwater tanks.
• Plants in planted tanks (without livestock) will only welcome high levels of nitrates.

Therefore, in the planted tank side of the hobby, we should never have 0 nitrates. Otherwise, if you don’t have some form of nitrates in your tank, your plants are suffering and don’t have anything to feed off. Nitrogen deficiency can be a very serious problem for planted tanks.

	Low	High
Shrimp tank	<10	>20
Fish tank	<20	>50
Planted tanks	<50	>150

I have to say that all those numbers are the result of a general consensus that hobbyists’ derived over years of experience and testing.

Although these numbers may vary depending on the tank set up, they can still be used to get a general estimation of whether the nitrate level is too high or not.

Aquarium Plants vs Nitrates

In the aquarium hobby, there is a popular idea that nitrogen in the shape of nitrate is one of the most important nutrients for aquatic plants.

Well, it is true but only to some degree.

Plants do absorb nitrates and can be a really unique form of chemical filtration that is much more effective than things such as carbon. Basically, plants are one of the essential filters for the aquarium.

But … what is the catch?

Lots of different studies show us that in reality, most aquatic plants prefer to use ammonia and ammonium to live and grow.

Plants rapidly detoxify ammonia and as NH3 enters their cells, it converts to non-toxic ammonium (NH4+). Another way plants use to detoxify ammonia is to synthesize proteins.

For example, Diana Walstad in her book Ecology of the Planted Aquarium (link to check the price on Amazon), says that aquatic plants take up ammonium more quickly. In the case of Dwarf Water lettuce, “the turn over” time was found to be 4 hours, while nitrates turnover required a full 20 hours.

Therefore, the fact that most terrestrial plants grow better with nitrates does not change the fact that for aquatic plants, nitrates are not their first choice.

Why Aquatic Plants Prefer Ammonium Over Nitrates

As a product of evolutionary development, aquatic plants rely mostly on anaerobic sediments, because this condition discourages nitrification.

Therefore, unlike terrestrial plants (where a high concentration of oxygen helps bacteria to convert ammonium to nitrates very fast), aquatic plants adapted primarily to ammonium-based nutrition.

However, it does not mean that aquatic plants will not take up nitrates in our tanks. But for that, they need to convert nitrates back into ammonium. The only downside is that it takes them a lot of energy to do so.

Which Aquatic Plants are the Best to Remove Nitrates

Without any fluff, these plants should meet 2 extremely important criteria, such as:

1. They must grow very fast. The faster the better.
2. They must feed from the water column. The plant should not be a root-feeder (planted into the substrate).

Plant’s growth is the main focus here. Because if plants do not grow fast, they do not absorb nitrates fast enough to create balance in the tank.

At the same time, we need to be careful with density. If you think that the more plants you add, the better the result will be – you are wrong!

When there are too many plants, they will compete for the nutrients. As a result, plants will not grow as fast as they can, or even worse, they will die because there is not enough food. As a result, the decaying plants will cause ammonia/nitrate spikes.

You can also read “Allelopathy or Warfare in Aquarium Plants”.

Also, you must understand that there two types of plants:

1. water column feeders (absorb nutrients primarily through their leaves)
2. root feeders (absorb nutrients primarily through their roots in the substrate)

Important: I am not saying that root feeders do not absorb nutrients from the water, it is just this is not the main way of feeding and they are less effective and should play a support role to maintain the system stable and safe.

Unfortunately, beginner aquarists often do not know or forget about these rules, as a result, they do not understand why the nitrates level in their heavily planted tanks are so high. I cannot stress enough to say that not all plants are great at absorbing nitrogen in our tanks.

Examples of Great Aquatic Plants to Remove Nitrates

Pothos Plants

Although Pothos plants are not exactly aquatic, they can still hold great benefits for your home aquarium. These plants are extremely hardy and make a great choice for people that lack experience with growing plants as they require minimal care to maintain.

However, most important, they are amazing at reducing nitrate levels. These plants combine the efficiency of terrestrial and flexibility of aquatic plants.

I highly recommend checking these plants!

 You can also read my article “How to Use Pothos Plants in a Shrimp Tank”.

Examples of Floating Plants:

• Hornwort, 
• Duckweed, 
• Water Sprite, 
• Water Wisteria, 
• Frogbit,
• Salvinia auriculata,
• Guppy grass,
• Dwarf Water lettuce, 

Because of their fast growth, floating plants consume a lot of ammonia and nitrates in the tank making the water cleaner.

For example, according to the experiments, Hornwort reduced ammonium and nitrate by more than 62% and 41.66% in 6 – 18 days accordingly. 

Note: Young plants, rather than older ones, are efficient in removing nutrients because they need these nutrients for their normal metabolic requirements.

You can also check out my article “Aquarium Floating Plants. Pros and Cons”.

Lighting, Filtrating, and CO2 vs Nitrates

It may sound strange how can lighting, CO2, and filtration effect nitrates? What is the correlation between them?

Lighting

First of all, any tank must be balanced in terms of light because this is the major factor that is going to help your plants grow!

Therefore, when plants do not get enough light they can get sick and eventually die out. So, instead of helping you to remove nitrates, they only add more waste.

Related articles:

• Advanced Guide to Planted Tank Lighting
• Light, CO2, and Nutrients: Why Aquarium Plants Struggle to Grow

Filtration

In order to realize photosynthesis, aquatic plants require the necessary quantities of nutrients in the water.

So, when we install powerful filters with great mechanical filtration (physical removal of particles from the water itself. For example, leftover food, fish feces, etc.), and chemical filtration (ammonia absorbing media), they come into direct “competition” with plants.

As a result, it makes plants weak and they don’t grow fast enough.

That is why it is very important to understand your tank setup. We have to know what works best in this or that situation. For example, if we use a small sponge filter in a big tank, it would be better to use some fast-growing plants to remove nitrates. If we use the topmost filter and our water is crystal clear, fast-growing plants can/will suffer.

CO2

CO2 is another factor that keeps the growth rates in a tank. So, the more CO2 you provide the more carbon the plants can use to create energy (glucose/sugar) in the photosynthesis period. 

A lack of CO2 can cause plants to suffer or grow abnormally.  Therefore, CO2 levels being too low can hurt your plants in the tank.

I would highly recommend reading my article CO2 in a Planted Tank Guide.

All these factors are crucial! If you want your plants to be happy, the tank must be balanced in terms of light, CO2, and nutrients.

Over Ways to Remove Nitrates

Nitrate absorbing Filter Media

Nowadays, we have filter media on the market for all occasions. For example, Seachem de❊nitrate™and Matrix (link to check the price on Amazon) will take care of the nitrate very quickly. In addition, Since de❊nitrate or Matrix are all biological support media, they do not ever exhaust, but they can grow less efficient with use by pore-clogging. Prefiltering the water before it passes through these products will extend its useful life.

Nitrate Reducing Pads

Personally, I have not had a chance to use them yet and there are lots of stories that they don’t work.

It seems like the main problem is that these nitrate-reducing pads usually do not have any instruction on how to use them. I mean how many pads we need to add into 10 or 20-gallon tanks, etc.

In addition, it really hard to say how exactly these pads work. Presumably, they contain some sort of nitrate-reducing chemicals that can absorb nitrates.

All I know is that we need to put them into the internal filter or external filter where water will flow through them.

Another downside is that they need to be replaced every few months.

Acurel Infused Media Pads for Aquariums (link to check the price on  Amazon)

Denitrators

Denitrators have particles that promote the activeness of microorganisms, which feed on nitrate and break it down biologically.

For example, Tetra NitrateMinus – Click to view on Amazon.

Can Seachem Prime Remove Nitrates?

No, Seachem Prime cannot remove nitrate from the water column. It simply binds with those compounds making them harmless to the inhabitants and still bioavailable to the beneficial bacteria.

Detoxification is not the same as removing it. It only provides detoxification for an emergency until you have time to do at least a water change.

Basic Tips to Control Nitrates in the Tank

1. Do regular water change.
2. Don’t forget to check your tap water to see if it has nitrates first.
3. Do not overfeed.

Do Water Changes

Unless you are running a No Water Change Tank (yes, it is real), you need to perform regular water changes.

Simple math – if I do 50% water change, I will remove 50% of the nitrates, if I do 30% water change, 30% of the nitrates will be gone, etc.

Water change is the fastest way to remove the nitrates; however, it can be risky for some setups.

For example, it is not recommended to do big water changes in the shrimp tank. Big water changes are often the reason for the “White Ring of Death”. Frequent water changes alter the parameters and make the shrimp undergo a forced molt.

Unlike shrimp, most species of fish can eventually acclimate to high nitrates. However, if a hobbyist decides to do a massive water change in an attempt to get rid of those nitrates, it can shock those fish in a similar way to a big pH swing.

So, what is better? What is the lesser evil then?

In my opinion, it depends on the nitrates levels. If they are moderately higher, I would just do water changes more frequently. Nonetheless, in other cases, the rapid reduction of potentially harmful toxins in a tank is of the utmost importance. 

Check Your Tap Water for Nitrates

Sometimes people do water changes but the nitrates are not going anywhere!

When you do water changes, check your tap water to see if it has nitrates first. It may already contain nitrates.

In this situation, you either need to use a reverse-osmosis unit, or you will have to buy suitable water for your aquarium.

Do Not Overfeed

We all love to feed our pets … sometimes too much … way too much. Overfeeding is probably the start of most of our problems in the first place. This is not overestimation! Take it very seriously.

In Conclusion

We all know that aquatic plants are not just decorative. It would be no exaggeration to say that they can have a fundamental role in reducing nitrates in our tanks.

Their unique form of chemical filtration allows achieving the natural balance. Even if your mechanical filtration fails they will be your second line of defense.

However, if you are looking for the best plants to remove nitrates, you have to choose pothos plants and/or fast-growing floating plants because they need lots of nutrients to keep up with their rapid growth patterns.