Good parameters, Good CO2, Good light, Poor plant growth?

I have good nutrient, CO2 and light levels, why do my plants still grow poorly ?

Many hobbyists spend time perfecting tank parameters, nutrient, light and CO2 levels, thinking that this automatically translates into optimal plant growth. While these factors are important, there are many other factors that affect plant growth.

For example above we have two groups of Lysimachia parvifolia growing side by side. Both groups have access to the same parameters, CO2, light, nutrients, substrate. However, the group on the right is growing poorly with darker, melting leaves and the group on the left is growing super vibrant red, with hardly a blemish.

This is not due to some arcane reason such as water flow hitting one group but not the other. The reason here is much simpler - the group on the right has been trimmed back repeatedly and allowed to grow in the same spot for a few months, while the group on the left was uprooted in the last month, divided and replanted. Overcrowding, both above and below the substrate, resulted in poorer quality new leaves being produced for the group on the right. This poor growth happened despite great growth parameters, a ton of CO2 and nutrients in the water column etc.

Different plants have different tolerances for overcrowding and aging. Some plant species regenerate well from repeated trimming cycles, others need replanting more frequently. Having great growth conditions delay deterioration of old growth, but most plants grow more optimally with regular replanting to clear congested rootzones and old growth. 

In this 4 month old aquascape, Rotala blood red sg (1) and Lysimachia nummularia 'aurea' (2) has never been replanted since day 1. They are very resilient towards trimming when growth conditions are good, and the bottoms can regenerate good growth even after repeated trimming cycles. They are also less affected by root zone congestion. 

However, Rotala macrandra mini type 4 (3) deteriorates quickly after a couple of trimming cycles. In this aquarium, it is uprooted and replanted monthly to keep the canopy in good form. This species thus need 5X as much replanting compared to Rotala blood red sg to keep it growing in good form. 

Trimming and replanting cycles

The exact number of trimming cycles each species can regenerate from, and the time it takes for old growth and root zone congestion to take effect is different for each aquarium. Generally, if aquarium conditions are more spacious, and there is more substrate depth and stable growth conditions, plants can grow in one spot longer. Stressful growth conditions, poor nutrient/CO2 levels and even poor microbial balance accelerate deterioration of old growth. 

Interestingly, on the opposite end, overcrowding and root zone congestion also happens more quickly in fast growth aquariums. Hobbyists that throw a ton of nutrients and CO2 at their plants run headfirst into the brick wall that is overcrowding. This can be countered somewhat by using a portion of slower growing plants in an aquarium. The slower growing plants can be worked less often, while the fast growers are on a more regular replanting cycle.

Many aquascapers avoid stem plants because they require much more frequent replanting to grow well. Species such as Anubias, Bucephalandra and Cryptocoryne species on the other hand, have extremely long replanting cycles, and can grow for years without needing to be uprooted.

In this stem plant heavy aquascape that is around 7 months old, every single plant cluster has been replanted at least once. A sample of the replanting cycle for each species:

• Rotala blood red SG - every 4 months
• Rotala macrandra mini type 4 - every month
• Lysimachia parvifolia - every 2-3 months
• Xyris difformis - every 5-6 months
• Elatine triandra - every month
• Rotala florida - every 3-4 months
• Staurogyne purple - every 5 months

Uprooting, cleaning, replanting:

To refresh stem plant bushes, we will replant the fresh tops of the plants, while discarding the older bottom portions. 

The first step is to uproot the entire stem plant bush. To control the mess when pulling up the soil, we recommend using a water siphon to vacuum the area when pulling up plants. The siphon should be held very close to the point where the plant is being pulled up to catch the soil debris.

Try to remove as much of the old root system as possible and also remove any organic debris that has accumulated in the area. While organic debris contributes small amounts of nutrients through decomposition, a build-up of organic debris will interfere with root formation for more delicate plants and will also trigger algae. To stir up the organic debris, we use a turkey baster to spray jets of water onto the substrate while vacuuming with a siphon. The aquasoil should look clean before we start replanting.

The next step is to sort the uprooted stems and select only the healthiest heads for replanting. (A) is a middle portion and already has several branches. The main stem is already aged. (B) is a weak cutting- observe how thin the stem is, and the lack of colour. (C) is ideal. A thick, singular healthy top with well formed new leaves. We will only replant tops that look like plant (C) and discard the rest.

Enriching the substrate with new aquasoil

When plants are uprooted, we can take the chance to enrich the substrate. There are two main ways to replenish depleted aqua soils. The first is to use nitrogen-rich root tabs. The second is to add fresh ammonia-rich aquasoil periodically. A good rate is adding 1% of new ammonia-rich aquasoil per month. For example, if you have 30kg of aquasoil in an aquarium, adding around 300 grams per month will work well. You can add new aquasoil during plant replanting cycles. Simply remove a portion of old aquasoil with a water siphon or spoon, then add and mix in the new aquasoil. This method may be cheaper than using root tabs in the long run

With consistent maintenance, aqua soils do not need to be replaced. The aqua soil in this aquarium is 1.5 years old APT Feast. Regular enrichment and clearing of detritus allows the substrate to perform like new. By renewing plant growth continually through replanting, and enrichment, planted aquariums also become more algae resistant. 

Reducing replanting work

Replanting entire planted aquariums regularly is not feasible for most aquarists. So having an aquascape consisting solely of fast growing stem plants can be a nightmare when overcrowding and age sets in. Aquarists should plant a mix of slower growing species and species that do not need frequent trimming/replanting. Then the fast growing bunches can be replanted on a rotation basis - only one species is replanted during each weekly water change for example. Replanting work requires skill and dexterity. It is often difficult for beginners to manage, until some experience is gained. It becomes much easier with practice and time.

In this aquarium, Rotala florida, Xyris difformis, Syngonanthus species are all plants that can grow for months without replanting.

Avoiding replanting work entirely?

To avoid replanting work completely, aquarists can also focus more on hardscape to carry the aquascape design. Anubias, Bucephalandra, Java fern and Cryptocoryne species are all slow growers that only require occasional trimming. These style of aquarium is much less maintenance intensive and it is a style many long term aquarists eventually settle on.