How to Spot Nutrient Deficiencies in Aquatic Plants

How to Spot Nutrient Deficiencies in Aquatic Plants

What Can Nutrient Deficiencies Do to Aquatic Plants?

Most of us want to have a lovely planted tank in our room. However, we cannot just add plants in the tank without providing them with the proper nutrients. Every planted tank has a unique set of requirements, some of which can be very tricky to get just right.

A lack of nutrients can cause discoloration in aquatic plants. Many types of nutrient deficiencies affect the ability of a plant to photosynthesize. This causes plants to start to discolor instead of being their regular green color. Leaves may change to a yellow, brown, or lighter green color. The leaves may also start to grow in incorrect shapes or start to twist. Not treating nutrient deficiencies can cause plants to die over time.

Keep on reading for everything you need to know about How to spot nutrient deficiencies in aquatic plants including background information, a detailed guide for the plants’ nutrition, in addition to other essential information pertaining to its usage in aquariums.

Phosphates (PO4)

Phosphorus is taken up by aquatic plant cells in the form of phosphate (PO4) and plays a vital role in energy transfer (from shoots to roots or from roots to shoots) and its compounds play a basic role in the mechanisms of photosynthesis.

Phosphorus is also responsible for the storage of energy in aquatic plants. Basically, when our plants melt (for example Cryptocoryne sp.), they will use this energy to grow back.

Recommended Levels

Phosphates are normally found in nature in small concentrations such as 0.01 mg/l. The phosphate levels in your tank should be in the 0.05 -1.5mg/l range.

If your levels exceed that range, you can expect your tank to experience excessive algae growth. Higher levels of phosphates may also affect the health of any fish in the tank.

How a Phosphate Deficiency Works and How to Combat it

Aquatic plants need small concentrations of phosphates to use as nutrients. Your tank can experience a lack of phosphates, which will affect the plant life in your tank. A lack of phosphates is normally uncommon because phosphates are an ingredient in fish food. If you feed your fish, you are also adding phosphates to your tank.

However, tanks with fewer fish may experience a lack of phosphates because you are not adding as much fish food. In addition, phosphate filters may also lower phosphates to where it starts to affect the tank. Adding monopotassium phosphate to a tank will help increase phosphate levels.

How to Tell If Your Plants Are Suffering from a Lack of Phosphates

You can tell if a plant is lacking phosphates because of delayed maturity and stunned growth, the leaves will begin to yellow or even may show purple coloring.

You may also see brown patches and the leaves may start falling off. In addition to the color changes, the leaves may also develop Green spot algae. The algae appear to break down the dying leaves.

Note: Young plants are particularly vulnerable to low levels of phosphorus.

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Magnesium (Mg)

Plants in our aquariums need magnesium because it plays a crucial role in photosynthesis. Magnesium is the central element in the chlorophyll molecule that is responsible for the absorption of the sunlight and the usage of its energy to grow.

In addition, Magnesium also serves as a phosphorus carrier in plants and helps in phosphate metabolism. The connection between these two elements is so close that aquatic plants cannot take up phosphorus and magnesium, and vice versa, unless both of them are present.

Recommended Levels and How a Magnesium Deficiency Works

The magnesium levels in your tank should be in the 5-10mg/l range. Magnesium is an important macro-element that is needed for photosynthesis. A deficiency of magnesium can cause the lack of a plant’s normal dark green coloring. This is due to the plant’s inability to photosynthesize like normal.

How to Combat a Magnesium Deficiency

You can add magnesium to the tank in order to raise the tank’s magnesium levels. Some liquid fertilizers also contain magnesium and they can be added to the tank as well.

How to Tell If Your Plants Are Suffering from a Lack of Magnesium

You can tell if a plant is lacking magnesium because the leaves will turn lighter and the veins will remain dark green. The lack of magnesium in plants can cause plants to stop developing as normal.

The older leaves are more likely to start turning yellow but the newer leaves will start growing in yellow as well. The normal growth will not return to the plant until the magnesium levels in the tank normalize.

Carbon Dioxide (CO2)

The carbon dioxide levels in your tank should be in the 20-25mg/l range. Carbon dioxide is an essential macronutrient needed for plants to photosynthesize. Without photosynthesis, plants can’t get the food and nutrients that they need. This causes the plant to start to die.

How to Combat a Carbon Dioxide Deficiency

Depending on your tank setup, you can make your carbon dioxide levels higher by setting a light timer to 8 – 12 hours a day. Allow the tank some time without light.

This slows down the photosynthesis process. In return, the carbon dioxide levels have time to build up again throughout the night. You can also switch out fast growing plants for slow-growing plants. These plants require less carbon dioxide to grow properly.

Tip: The Walstad Method recommends to turn the lights off for 3 – 4 hours in the midday as well because aquatic plants take up almost all the CO2 by noon. Therefore, during the siesta time, it will allow CO2 levels to regenerate once more. So, when you turn the lights on the plants will have CO2 again.

This schedule may look like – 5 – 6 hours on, 3 – 4 hours off, 5 – 6 hours on. It will provide your plants with carbon dioxide and improve the plants’ growth. As a bonus, it will also help with algae control.

How to Tell If Your Plants Are Suffering from a Lack of Carbon Dioxide

A carbon dioxide deficiency can cause leaves to weaken or grow in weird twisted shapes. The leaves also start to discolor because the plant can’t photosynthesize properly. The leaves turn pale or yellow over time. If the plant continues to be unable to photosynthesize, it will start to die.

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Nitrogen (N)

Nitrogen is a natural part of ecosystems in our tanks. Plants use it primarily to synthesize protein. Nitrogen can enter the ecosystem in several chemical forms and also occurs in other dissolved or particulate forms, such as living and dead matter.

Interesting fact: Although aquatic plants can absorb and use nitrogen in all forms (nitrates (NO3)), nitrites (NO2), ammonia (NH3)), many plant species still prefer ammonium (NH4+). If there are ammonium and nitrates present in the tank, they will always ignore nitrates and take ammonium first. Ammonium is the fastest way of getting nitrogen into a plant’s system. That is why they do not have to spend energy converting it to the form it uses.

Recommended Levels and How a Nitrogen Deficiency Works

The nitrogen levels in your tank should be in the 5-25mg/l range. Nitrogen (Nitrate) deficiency is also an extremely common problem in tanks. However, in most cases, you do not have to worry about a nitrogen deficiency if your tank contains fish and/or snails.

However, planted tanks will start to experience adverse side effects when nitrogen levels get too low. Nitrates are present in the waste of your livestock (fish, snails, crabs, shrimp, etc.).

Note: Keep in mind that, it also depends on what you have. For example, dwarf shrimp do not produce a lot of waste, while snails are waste factories. Some animals have more significant bioload than others.

If there are not enough fish, plants in the tank will not get the correct number of nitrates that they need for nutrients. Having too many fish and not enough plants in a tank can commonly cause this problem.

Routine water changes may also cause the deficiency because you get rid of some of the nitrates currently present in the tank. If you do water changes without measuring your nitrogen levels, you may unknowingly trigger a nitrogen deficiency in your tank.

Using the wrong amount of fertilizer in your tank may also cause nitrogen to decrease. Plants should be given more fertilizer as they grow larger but many people stick to the original feeding amounts. If there is not enough fish waste and not enough fertilizer, then your plants will lack the phosphates that they need.

Important: There is also a very fine line between safe and dangerous nitrogen levels for your pets. For example, shrimp are more sensitive, therefore, you have to take it into consideration.

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How to Combat a Nitrogen Deficiency

Increasing the amount of fertilizer used in your tank can help nitrogen levels normalize. You can add KNO3 (potassium nitrate) to the tank directly to increase nitrogen levels as well.

Tip: If you do not enough fish to produce a lot of waste, you can add fish food anyway to improve nitrogen deficiency in the tank. Of course, it is not the best way to fix the problem because it also adds other chemicals as well as the nitrogen, which can promote algae and foul the water in the tank.

Important: Unless you are an experienced aquarist and have some knowledge about planted tanks and how nitrogen can affect your livestock, you should treat ammonia, nitrates, and nitrites as enemies, not as friends.

How to Tell If Your Plants Are Suffering from a Lack of Nitrogen

A nitrogen deficiency (not enough protein) can cause your new leave to become smaller and older leaves to start to yellow. This yellow discoloring usually starts at the tips and move to the base of the leaves. This is the plant’s way of using the older leaves as nutrients for new leaves growing in. The new leaves will appear light green.

Potassium (K)

In terms of the amount of nutrients, the aquatic plant needs for growth potassium is second only to nitrogen. Potassium supports and activates of over 80 plant enzymes responsible for:

  • improving a plant’s water use from roots to shoots
  • the regulation of photosynthesis and respiration
  • increases nutrient uptake
  • enhances nitrogen use
  • increases protein production

All in all, potassium is extremely important in our aquariums, it boosts the plants’ health and the

plant’s ability to withstand disease, pests, and stress.

Recommended Levels and How a Potassium Deficiency Works

The potassium levels in your tank should be in the 5-10mg/l range. Potassium is a macro-element which helps keep plant ions in balance. It also helps with osmoregulation.

Tap water normally does not contain enough potassium to benefit aquatic plants. A deficiency in potassium is normal when potassium isn’t manually added to a tank.

Depending on the source you add the potassium, Carbon filters can make the problem worse because they add carbon to a tank. The carbon levels are linked to the potassium levels. Due to the increase of carbon, the potassium levels of the tank drops.

How to Tell If Your Plants Are Suffering from a Lack of Potassium

You can tell that potassium levels are low if your plants begin to develop holes that are outlined with black or yellow color. The leaves can melt away in the yellow area as well.

You may also see dying leaf tissues or the root system of the plant may struggle to form correctly. Leaves may also fall off in extreme cases.

Example: Seachem Flourish Potassium (link to check the price on Amazon).

Note: It is safe for the shrimp and carbon in the filter does not remove Flourish Potassium.

Calcium (Ca)

Calcium is also a very important element for that aquatic plants. It acts as a regulator of osmotic pressure in a plant. It stabilizes the elements of membranes and strengthens the cell walls.

Recommended Levels and How a Calcium Deficiency Works

The calcium levels in your tank should be in the 20-30mg/l range. Calcium is another macro-element and it is crucial to regulating various cell processes. Calcium is also a part of a cell wall.

A calcium deficiency is closely linked to a tank’s water hardness. Tanks with soft water are the only tanks that can experience a calcium deficiency.

How to Combat a Calcium Deficiency

You can fix a calcium deficiency by adding crushed coral into your filter. You can also add the coral directly into your substrate.

Another option to combat this deficiency is to add wonder shells, chicken eggshells, tums, calcium blocks, etc. into your tank. Using these solutions will cause your water hardness to increase, as well as increasing calcium levels.

How to Tell If Your Plants Are Suffering from a Lack of Calcium

Plants that are suffering from a calcium deficiency will experience difficulty growing. This also applies to the root systems of the plants. The leaves may also grow irregularly, forming twisted shapes. Deformation is extremely common and the plants may not grow to their regular size. The leaves of the plants may also turn brown.

If you keep shrimp, freshwater crabs, crayfish or freshwater snails in the tank, do not forget that calcium plays a huge role for the shrimp. Therefore. I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.

Iron (Fe)

Last but not least in the list of nutrient deficiencies in aquatic plants is Iron. Actually, this is one of the most common deficiency since it is not particularly stable in water and tends to precipitate out unless it is dosed frequently.

Recommended Levels and How an Iron Deficiency Works

Iron is a microelement. The iron levels in your tank should be in the 0.05-0.02mg/l range. Iron helps with the chlorophyll synthesis process. When a plant has an iron deficiency, you can expect discoloration because the chlorophyll synthesis is reduced.

How to Combat an Iron Deficiency

In order to raise micronutrient levels, you can also add dry or liquid fertilizers that contain iron.


How to Tell If Your Plants Are Suffering from a Lack of Iron

If your plants are suffering from a lack of iron, you can expect their coloration to be different than normal. The leaves will begin to turn a lighter green and the veins will stay the same deep dark green.

What Fertilizer Do You need?

There are a lot of different fertilizers on the market and it can become quite confusing which one to use.

For example, Seachem alone has a huge line of different fertilizers. Do you need all of them?

Well, no. In my opinion, Iron and Potassium are the most problematic nutrients in our tanks, therefore, another option is to buy all in one fertilizer.

In addition, if you have shrimp and snails in the tank you have to be especially careful because they are very sensitive to copper which is a quite common component in fertilizers.

You can also read my article “Shrimp Safe Plant Fertilizers”. 

How to Spot Nutrient Deficiencies in Aquatic Plants chart

In Conclusion

A lot of people, when they get into the planted tank hobby, they research: what are the best substrate, the lighting requirements, and CO2 systems. Actually, this is really great and they are doing the right thing. The problem, though, is that they often forget about fertilizers.

However, plants need vitamins and proper nutrients to survive. It is also a way to maintain your plants and make them grow a lot better.

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How to Spot Nutrient Deficiencies in Aquatic Plants

3 thoughts on “How to Spot Nutrient Deficiencies in Aquatic Plants

  1. Hi Michael,

    You’ve given us so much information here. It would have taken me years of trial and error, research, and horticultural death by ignorance to come up with some of this. And there’s so much online info that may or may not be trustworthy; I feel like I can trust you somehow. That’s saying a lot from me. I have a biology degree and I am a vicious skeptic. With your help, I’m convinced that by treating my poor snails’ troubles, I’ll help my goldfish, and save my floating plants, as well as resolve some other issues I’m sure I e caused by my ‘research’.

    I used products to bring my water right down to a perfectly neutral pH. Yay me. Early killed killed one mystery snail and had another escape the pond and glide three feet over soaking wet cocoa mulch. He was halfway to the mucky recovery pond I’ve been tossing my sad, browning hyacinths in.

    So, I will work to resolve the calcium problem hopefully fixing the pH and hardness issues, while watching the potassium levels and keeping any carbon in the filter instead of in floating bags. Phew. You have saved me soooo much grief. Thank you again. I will try some of the home/cheap remedies first, but if there’s something that I can wait a couple of days for I WILL be clicking your links. Thank you so much!

    1. Hi Suzy,
      I’ll be glad if this information can help you!
      Nonetheless, if you have any specific questions, you can ask me anytime.
      Best regards,
      Thanks for the kind words 🙂

  2. Thank you very much. Every now and then I’m lucky to find priceless detailed info like this. I appreciate you taking the time to put this together and putting it on the internet for public accessibility.
    This is my ‘go-to’ database for my plants.

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