Why are my plants melting? Are plants melting in a new planted tank normal?

Why do aquatic plants melt?

Melting in this scenario refers to aquatic plant losing some or all of its leaves; this usually happens to older leaves first, which lose color and become transparent before disintegrating. 

Above: Hygrophila sp. Chai is notorious for melting. Melting occurs as plant cells adapt to new environmental variables; the plant channels energy into new growth and the formation of new proteins optimised for the new environment, sacrificing and scavenging nutrients from older leaves and discarding old DNA not optimised for the current environment. The sacrifice of older tissue occurs because the plant cannot meet its immediate metabolic needs and prioritises channelling energy into new, optimised growth.

One of the biggest changes between emergent and submerged growth is reduced access to the gases CO2 (carbon dioxide) and O2 (oxygen). Due to the poorer gas exchange in water, sudden submergence of an emergent aquatic plant cuts off its access to CO2 and O2, putting the plant under enormous stress. Plants must compensate quickly or die, diverting all energy into new, submerged, adapted growth while sacrificing energy needed to maintain older growth. Many species would also attempt to break through the waterline and regain access to air by increasing their internodal distance. The provision of CO2-enriched water will greatly assist this transition stress.

Melting can also occur as a result of prolonged poor growth conditions, resulting in fragile plants that melt easily when pushed over the edge by small changes in environmental conditions. This usually happens in tanks where the nutrient dosage has been too low for a long time, resulting in plants that look fine on the outside but are actually very fragile - in this state, any sudden change in the environment can tip it over and cause it to melt.

Is melting normal and unavoidable in new tanks?

Contrary to popular belief, melting is not normal or inevitable. However, it is extremely common, especially in new aquariums or aquariums without CO2 injection. Some species, such as Cryptocoryne species, as well as delicate plantlets from tissue culture, are particularly prone to melting when adapting to new tanks, but even this can be minimised or avoided if you know what variables to control.

In principle, if growth conditions are favourable, there is no need for a plant to sacrifice old tissue to divert energy to new growth. If the plant can get what it needs directly from the environment, both to grow new leaves and to maintain the older ones, there would be less impetus to melt. The same emersed leaves of many species (Cryptocoryne, Bucephalandra) can transform directly into submerged leaves. In good conditions, many plants can maintain their submerged form leaves underwater for many months, although they perform less effectively than newly grown, fully submerged adapted leaves.

Tissue culture plants are very inexpensive because you can get many plants from a single cup - that is, if you manage to grow out all the small plantlets. They are more delicate than full grown plants and are particularly sensitive to immature aquasoils or soils with a lot of detritus. Avoiding transition stress allows their value to be fully exploited.

Back in 2018, Cryptocoryne flamingo became more readily available in Singapore in Dennerle tissue culture cups. With good tank conditions, it was possible to grow out 15+ plants from a single $30 cup. 

Avoiding plant melt, easing transition stress

Melting occurs as the plant adapts to new environmental variables. Preventing melting involves a two-pronged approach of reducing plant stress and giving the plant good growth parameters;

1. Get healthy plants to start with; plants with more stored energy have more energy to cope with the transition process. Weak plants and finicky species are more susceptible to melting. Long transport and poor handling also affect plant health, so who you buy plants from is critical.

2. Get high O2 & CO2 levels. The main stress factor in moving plants from emersed to submerged is that they are suddenly in an environment where it is much harder for the plants to get CO2/O2, as gas exchange is much poorer under water. These elements are at the heart of a plant's metabolic processes and carbon makes up more than 50% of a plant's dry mass, more than any other 'fertiliser'.

3. Plant in a mature tank. This is especially true for users who use ammonia rich aquasoils. Ammonia is harmful to plants in large quantities. Cycling the tank beforehand allows VOCs to settle and is less stressful for the plants. Have you failed to grow Utricularia gramminifolia from tissue culture? It is most likely because this step was skipped. UG is otherwise an easy plant to grow.

4. Remove organic debris from the substrate for rooted plants. Too much organic matter rots delicate plants such as those from tissue culture. It also causes algae problems in the tank as a whole.

5. Use lower temperatures for your aquarium. Lowering the temperature slows down plant metabolism and therefore the demand for CO2/O2/nutrients. 22/23 degrees Celsius works well.

6. Separate large clumps of plants and plant in smaller groups. This allows for better water flow around individual plants, less overcrowding and better access to light.

7. If you are not already dosing a broad spectrum liquid fertiliser into the water column, you should do so. New plants have undeveloped root systems and cannot take up nutrients from the substrate. But they can still draw nutrients directly from the water column. People who delay dosing in new tanks are not helping their plants to acclimatise. Dosing should be done from the first day the plants are introduced into the tank.

Hygrophila sp. Chai is one of the rare plants readily available in tissue culture form. However, the majority of hobbyists fail to convert the tissue culture to submerged form because it is delicate. For finicky species, in addition to following the steps above, planting in open areas with good access to light and water will increase the chances of success. The area 2 inches from the front glass of the tank is the most favourable area in most tanks as it has higher light levels (internal refraction of light from the front glass) and good access to current (downwash from current hitting the glass) with no taller plants to block the area.

What if I have a low tech (non CO2 injected) tank ?

Without CO2 injection, a major stress factor (access to CO2) cannot be mitigated. This is why smelters are so common in tanks without CO2 injection. However, the other variables still apply. Getting submerged, robust plants will help. Choosing species that are hardy and suitable for non CO2 injected tanks will improve success rates tremendously (Java fern, crypst, anubias). Most low tech tanks have lower overall light levels, you may want to choose open, unshaded areas to plant sensitive species so they get more light. Flow is still important - good circulation in a tank improves gas exchange and brings dissolved gases to the plants. If you are not dosing the water column, dosing an all round fertiliser is effective; freshly planted plants can take up nutrients directly through their leaves, even if their root zone has not yet developed to feed from the substrate.

Also, in non CO2-injected tanks, the transition will generally take longer. Patience is required and resisting the urge to move plants around will allow them to settle and acclimatise to their position in the tank.

I have a tank that was running perfectly fine and suddenly I have some plants melting, what can cause this. I did not change my light/dosing/CO2 etc?

This usually happens in tanks that use very low dosing methods over a long period of time. Plants that have been underfed for a long time may appear to be intact, but are in fact very fragile. The slightest shock to the system will cause them to melt. Often there are subtle signs of long-term nutrient deficiency in such tanks (along with minor but persistent algae problems). Intermittent melting in an otherwise stable tank could be an indication that the dosing methods are not robust enough;

This is more common in approaches where the tank is heavily dependent on substrate feeding of the plants. As the substrate is depleted over time, the plants that were dependent on the root substrate will become less robust over time. If your aquarium relies on substrate feeding to grow plants, it is important to enrich the substrate over time. Many aquasoil substrates deplete much faster than people realise, with the majority of nutrients being used up in the first few months of submergence.

What do I do if I already have melting plants?

Remove dead/dying tissue; this removes ammonia/pollutants from the tank and gives existing leaves more room to grow. More water changes to remove ammonia and dead and dying foliage will reduce algae outbreaks; better water quality will always help plants to settle in.

In mature tanks, it is important to cut and replant new top growth and discard old growth, and to ensure that fertiliser dosage levels are adequate for long-term healthy growth.

In new tanks, paying attention to the biological maturity of the tank, making more water changes and ensuring low levels of organic waste will help. Adjust parameters to promote growth (check CO2, nutrient levels).

Head here for video on how to water change.

Here here to read the details on how to cycle a tank.

Head here to learn about The 2Hr Aquarist APT Fertilizers.