Does my plant have a nutrient deficiency?

What do plants need?

Like terrestrial plants, aquatic plants need a supply of nutrients to grow well. This has been well studied in terrestrial science and the chemical elements required for growth can be divided into two main groups:

Notable macro nutrients

CARBONmakes up the majority of plant mass, followed closely by nitrogen, then potassium and the rest of the macro-nutrients. Plants use more than 20 times the mass of carbon compared to nitrogen. This is why CO2 injection has such a big impact on plant growth results. So, for example, a tank that is rich in NPK but poor in carbon will not be helped by pushing NPK levels higher and higher if the carbon limitation has not been broken.

NITROGENis found in chlorophyll, nucleic acids and amino acids; it is a component of protein and enzymes. Nitrogen deficiency can increase the red colouration of certain plants by delaying the production of chlorophyll. Nitrogen availability has a significant effect on plant growth rates. Extreme restriction of nitrogen can cause growth rates to stall and plants to become brittle and fragile in the long term.

PHOSPHORUSis an essential component of DNA and RNA, which play a critical role in cell membranes; it also plays an important role in the energy system (ATP) of plants. PO4 is often under dosed in the aquarium. Plants with a good supply of phosphorus are more robust and some will show better colouration.

POTASSIUMplays an important role in plant metabolism and is involved in photosynthesis and protein synthesis. It is a very mobile nutrient. The overall health of the plant deteriorates when it is deficient. Common symptoms include yellowing, pinholes and brittle leaves.

MAGNESIUMis part of every chlorophyll molecule, which plants use in photosynthesis to make food.

Notable micro nutrients

IRON, in the form of both Fe2+ and Fe3+, is absorbed by plants, but plants would have to expend energy to reduce Fe3+ to 2+ before absorption. Iron is responsible for the formation of enzymes involved in chlorophyll production, and when a plant is Fe deficient, chlorophyll production is reduced, resulting in the characteristic symptoms of leaf chlorosis. (yellowing of leaf tips).

MANGANESEis involved in the photosynthetic process of plants and deficient levels of Mn result in reduced photosynthesis and growth. Sub-optimal levels can also result in curled leaves (although many other factors can cause this). This is an example of how missing/deficient micro-nutrients will affect overall plant growth - and the uptake of subsequent macro-nutrients such as NPK. So micro-nutrients are very important, even though they are only needed in trace amounts.

BORON, ZINC, COPPER, MOLYBDENUM, these are all important for plant growth, albeit in minute amounts.

OTHERS; Other macro-nutrients include sulphur, oxygen, hydrogen; these are usually readily available in tap water or soil. Certain species may benefit from additional micro-nutrients; silica (Si), vanadium (V), selenium (Se), cobalt (Co). These are not classified as essential - their use in plants is not fully understood, although terrestrial studies show that certain crops show increased yields when they are available. Many trace mixtures contain them. The micro traces of silica, chlorine are common in tap water and most substrates.

Using 'deficiency charts' - or rather why not to

These charts are derived from agricultural diagnostics and are terribly inaccurate for aquatic plants. Many different problems can cause yellowing leaves or stunting. Inadequate CO2 causes many symptoms that look similar to common 'nutrient deficiencies', including premature leaf drop or yellowing, loss of colour and stunted leaf tips. This means that many people misdiagnose their problems by trying to match the symptoms to those shown on deficiency charts.

Nutrients also work synergistically - none of them work in isolation. To find out what is lacking in a tank requires an analysis of the holistic approach to tank management - not just trying to spot a yellow leaf here or there.

Most of the time people use these charts to confirm existing biases. These charts also lead to nutrient tunnel vision - the idea that any and all poor growth is a result of nutrient problems. When in fact there are a host of other issues that can affect plant health. These include CO2 saturation levels, water parameters (especially KH), overall tank stability, organic waste levels, substrate quality, whether you are using the correct pruning methods for certain species etc. If people keep thinking it's nutrient related - especially if they're already dosing... then they keep looking for the wrong cause, which means they'll never solve their problems.

There is also a huge gap between sufficiency and optimality. For example, to prevent phosphate deficiency symptoms in a particular plant, it may be necessary to dose 0.1ppm of phosphate per week. However, to get it into great shape it may need 3ppm + per week instead. We should be aiming for the latter (to grow great plants) rather than the bare minimum for plant survival and the gap between these levels can be huge. These charts will not get you on the road to growing great plants.

"It is a chronic newbie-intermediate urge to get focused on deficiencies, even when they're following EI (!!). I used to think all my issues were lack of something or another and when you find charts like this, it temporarily confirms existing biases. You figure your issue is K deficiency. You add K2SO4 but nothing gets better. Then what? Then it's time to focus on other stuff. I've found many clever ways to kill and stunt plants, especially Rotala and Ammannia. Deficiencies are low down on the list. Poor maintenance and poor CO2 are big reasons." - Vin kutty 

"Grow the plants, not the deficiencies. The method is deceptive as it is simple." - Tom barr

These Glossostigma elatinoides are grown under light nitrate limitation. Yellowing of the outer leaf margins is an indication, but can only be confirmed by checking the tank parameters and dosing method.

Diagnosing issues - First step; rule out as many factors as possible by having a regular, holistic dosing schedule

Start with a good baseline of holistic nutrient dosing (see the section on nutrient dosing). A regular regime is necessary for analysis - if you tweak every other day, there is no baseline on which to base your observations.

Next, optimise your CO2 levels. Drop checkers are not an accurate measure of CO2. It is not as simple as increasing the injection rate - this is probably the hardest part for most aquarists to get right as it involves adjusting flow patterns, gas exchange and rethinking diffusion methodology. CO2 levels have a huge impact on plant growth and health - this is especially true for difficult species.

Next, check that you do not have extreme water parameters. An easy way to rule this out is to look at people in your country/area who use the same tap water. Are they able to keep sensitive animals? If they are, chances are your tap water isn't that bad. Check your GH/KH levels and see if you are growing plants suitable for that range.

Then tweak the nutrients one at a time for further optimisation.

To get a better idea of what is happening in a tank, you need to know the existing parameters and therefore what is likely to be the cause, i.e. if you have 50 ppm potassium in the water and still get yellowing holes in the leaves, the problem is definitely not K related. If you are adding more than 0.1ppm chelated Fe per day to a tank - you can safely rule out iron deficiency. Nutrient problems are really not that difficult to rule out. This is largely because plants regulate their growth to match what is available; lean conditions do not lead to immediate deficiencies - they just lead to slower growth. True deficiencies take time to develop. The hard part for most aquarists is accepting that in most cases poor growth is caused by non-nutrient factors. This is also why many aquarists can spend years tweaking their dosing schedules and still end up with pretty mediocre looking plants at the end of the day. Focusing on non-nutrient factors such as plant husbandry or CO2 is just as important as a holistic approach to nutrient dosing.

Using plants as indicators; Fast growers vs slow growers

Fast-growing plants (such as most stem plants), especially coloured stems, are good indicators of past/present conditions. Look at the size, colour and shape of new leaves. Even in fast-growing plants, deficiencies take a while (a few days to a week or more) to appear. Melting and rapid deterioration of plants is never nutrient related.

• Are new leaves larger/consistent size (good) with old growth or smaller/stunted (usually a CO2 issue, or possible macro nutrient insufficiency)
• Is coloration consistent or uneven (may hint at immobile nutrient issues)
• Are the leaves smooth & well formed (good) or twisted (Inconsistent CO2, ammonia, KH, excessive fe/trace issues)

For old growth you can look for

• Are they much paler/yellow or with pinholes compared to newer growth (possible mobile nutrient (NPK) deficiency, but also often caused by poor or unstable CO2)
• Discoloration; veins are green but leaf tissue is pale/yellowish (could be Mg deficiency)
• Very quick deterioration of old growth even though new growth seem perfectly formed - hints that unstable tank parameters
• Persistent algae on old leaves; tank cleanliness issue, other stress factors, tank's biological maturity may need more time

Slow-growing plants such as Anubias and Bucephalandra are not good gauges of recent conditions, but are good long-term indicators because their leaves last a long time. They are a good test of general tank stability, not only in terms of parameters but also in terms of the hobbyist's habits.

Fast-growing stems such as these few varieties of Rotala macrandra need consistent all round fertilisation to maintain their vibrant colour.

These Anubias show signs of long-term magnesium deficiency. To get to this state requires a prolonged period (months) of magnesium deprived growth.

Bucephalandra species are a good test of long-term consistency and dosing method as they grow slowly. Leaves last for many months; fluctuations in tank regime and poor/unstable nutrient / CO2 levels will cause premature shedding of old leaves as the plant constantly re-programs its enzymes to suit current conditions.

Without optimal CO2 levels, diagnosing nutrient issues becomes difficult

CO2 is required for many picker plants to grow properly. Many plant problems are related to low CO2 or poor CO2 stability - without a solid baseline it is much harder to diagnose problems. The two Alternanthera reineckii below may be receiving the same amount of nutrients, but poor CO2 levels and a less than ideal light spectrum are causing the one on the left to be in poor condition - it's not a nutrient problem at all.

Similarly, the Alternanthera reineckii below is not suffering from a lack of nutrients. Instead, it is suffering from toxicity - either from too high a dose of trace elements, or from other harsh chemicals.

For an example of why concepts are not so simple, Rotala rotundifolia and its variants turn red when nitrogen is limited. N limitation delays chlorophyll production in new leaves of Rotala rotundifolia. If done in a controlled manner, this will not harm the plant and will not cause premature deterioration of old leaves. However, new growth will appear significantly redder.

In the photo above you can see the exact point where the tank became N-limited. (This is where the new leaves on Rotala rotundifolia turn red rather than green).

The pale new tips (sometimes even white as below) are often associated with iron deficiency. This can also be caused by other mechanisms that interfere with immediate growth. Iron is an immobile nutrient, as are many trace elements and calcium. Surprisingly (or not), CO2 is by far the most important factor affecting new growth - most new tip stunting is due to sub-optimal CO2. CO2 must be present throughout the light window as photosynthesis takes place.

Changing nutrient dosing approaches

If you suspect that a particular nutrient is lacking in the tank, you can add extra amounts of that nutrient and see if it has an effect. It will take a week to see any changes for sure, and some slower growing or previously stunted plants may take weeks to adapt to a new regime.

The irony of nutrient dosing is that many tanks actually stabilise and do better with less. So for people who are used to very high dosages, reducing dosages can be surprisingly fruitful.

Additional dosing has diminishing returns. In a very nitrogen-limited tank, the first 5 to 10ppm of NO3 added will have a big effect on growth/uptake rates, but additional doses will have a much smaller effect. Where true deficiencies are concerned, it should not take a large dose to make a difference. This is because the plants would have slowed their growth rates/metabolism to match the lean conditions. (not much growth = very little nutrient uptake)

Extreme ratios also tend to be ineffective. If you are dosing only 10ppm of nitrates in a week for a particular tank (and there are no other sources of nitrogen). It is extremely unlikely that it would consume, say, 40ppm of potassium. So if you suspect a K deficiency - it would be ruled out for sure if you were dosing 40ppm of K per week.

Growth forms change with nutrient levels. Richer conditions will generally produce larger, more robust forms. Robust plants are easier to transfer to other tanks/conditions and have more energy to adapt.

However, higher NO3 levels mean less reddish pigmentation for species that become redder under low N conditions. Lean conditions also result in smaller or more compact forms for some plants.

If you are increasing the dosage to try and get faster growth (bearing in mind both that there are diminishing returns - and that more is not always better), these are the upper limits of the range I wouldn't exceed in a week;

• NO3 - 50ppm
• PO4 - 10ppm
• K - 50ppm
• Mg- 10ppm
• Fe - 4ppm

Just for comparison the nutrient dosage per week for our farm tank above is as follows: 

• 18ppm K
• 7.7ppm NO3
• 3.4ppm PO4
• 2ppm Mg
• 0.15ppm Fe/traces

As you can see, it does not take all that much to fulfill the nutrient requirements of a very high light, densely planted tank.

Head here to learn more about optimizing CO2 levels.

Head here to learn more about water parameters.

Head here to learn more about ideal light spectrum.