Hemianthus Cuba (*Hemianthus callitrichoides* ‘Cuba’), often simply called ‘Cuba’, is one of the most sought-after, yet also most demanding, carpeting plants in aquascaping. Its ability to form a dense, bright green carpet resembling a lawn makes it a central element in many competition aquariums. However, to achieve such a result, the aquarist must create ideal conditions, primarily ensuring a high level of lighting and a stable supply of carbon dioxide (CO2).
Hemianthus Cuba: The Path to the Perfect Aquarium Carpet
Growing Hemianthus Cuba is an indicator of an aquarist’s skill. This plant does not forgive care mistakes. While other carpeting plants can exist in medium-tech conditions, Cuba requires a High-Tech aquarium. Success depends on the precise balance of three main factors: light, CO2, and nutrients.
To create the ideal carpet, it’s important to understand that Cuba is not just decoration, but a living organism with a very high metabolism that constantly competes for resources, especially in a densely planted aquarium.
Hemianthus Cuba Biology: What Beginners Need to Know?
Hemianthus Cuba is the smallest known aquarium stem plant. Its tiny, rounded leaves and delicate stems allow it to hug the substrate closely, forming a low (up to 3 cm) and dense carpet.
- Origin: The plant was found in Cuba, near Havana, which gave it its species name.
- Growth Type: Carpeting, spreads along the bottom. It propagates by lateral shoots (stolons) that root quickly.
- Nutrient Requirements: High. Actively consumes both root and foliar nutrition.
- Feature: The plant easily transitions from its emersed (above-water) form to its submerged (underwater) form, which is often used in the Dry Start Method (DSM).
Important: When purchasing the plant, ensure it is already in its submerged form, or use DSM, as the transition from emersed to submerged can take a long time and be accompanied by partial leaf die-off.
Light – The Key to Growth: Choosing and Adjusting Lighting for Hemianthus Cuba
Light is perhaps the most critical factor for Hemianthus Cuba. Insufficient light leads to stem elongation (etiolation) and the inability to form a dense carpet. The plant will start to grow vertically upwards in search of a light source.
Cuba requires intense light. Experts recommend focusing not on the outdated Watt per liter (W/L) metric, but on the PAR (Photosynthetically Active Radiation) value, measured in micromoles (μmol/m²/s).
Recommended Lighting Parameters
- PAR Intensity: At the substrate level, at least 50–70 μmol/m²/s should be provided. In aquariums over 40 cm high, a very powerful light may be needed to achieve these values at the bottom.
- Wattage: In W/L terms, this usually corresponds to 0.8 – 1.2 W/L (when using modern LED systems).
- Photoperiod: The optimal duration is 8–10 hours. It is recommended to use a timer for consistency.
- Spectrum: Full Spectrum with emphasis on blue (440–460 nm) and red (640–660 nm) peaks. A color temperature in the range of 6000K–8000K provides the best growth and a pleasant green color.
Practical Tip: If you notice Cuba starting to bubble (photosynthesize) 1–2 hours after the light turns on, it’s a good sign that the intensity and CO2 are in balance.
CO2 – Necessity or Luxury? Carbon Dioxide Supply System for Hemianthus Cuba
For Cuba, CO2 is not a luxury but an absolute necessity. With the high light intensity this plant requires, its metabolism accelerates to such an extent that the natural CO2 dissolved in the water becomes critically low. Without additional carbon dioxide supply, Cuba will slow its growth, begin to wither, and algae will take its place.
Setting Up a CO2 System
For reliable growth of a dense carpet, a pressurized CO2 cylinder system is necessary. Using “braga” (fermentation) or liquid carbon (e.g., Glutaraldehyde) is insufficient to meet Cuba’s needs under high light.
- Target Concentration: Maintain CO2 levels between 25–35 parts per million (ppm). This is sufficient for maximum photosynthesis without harming most aquarium inhabitants.
- Monitoring: Use a Drop Checker with KH4 reagent. The ideal indicator color is bright green or lime green. Yellow indicates overdose, blue indicates deficiency.
- Injection: CO2 injection should begin 1–2 hours before the lights turn on and stop 30–60 minutes before the lights turn off, to ensure maximum gas availability during peak photosynthesis hours.
- Diffusion: Use a quality diffuser or atomizer to produce the smallest bubbles and maximize gas dissolution in the water.
Attention to Fish: At CO2 concentrations above 40 ppm, fish may begin to experience oxygen deprivation. Ensure good circulation and aeration during nighttime.
Substrate and Nutrients: Creating the Ideal Environment for the Root System
While Hemianthus Cuba can absorb nutrients from the water, a nutrient-rich substrate is critically important for forming a dense and healthy carpet.
Choosing a Substrate
The best choice is an active nutrient substrate (e.g., aquasoil like ADA Amazonia, Tropica Soil, or similar). These substrates have a high cation exchange capacity (CEC), buffer pH (lowering it to 6.0–6.8), and contain all the necessary macro- and micronutrients for initial growth.
- Substrate Layer: A layer of at least 4–6 cm is recommended for reliable rooting.
- Nutrient Underlay: If inert sand or gravel is used, a nutrient underlay (e.g., lava gravel or specialized tabs) must be added beneath it.
Liquid Fertilizer Dosing (EI Dosing)
Under intense light and CO2, the plant quickly depletes water reserves. Regular dosing of macronutrients (NPK) and micronutrients (Trace Elements) is necessary.
Key Elements for Cuba:
- Iron (Fe): Iron deficiency leads to yellowing (chlorosis) of young leaves. Iron should be dosed daily or every other day.
- Nitrates (NO3) and Phosphates (PO4): Should be maintained at a ratio optimal for algae prevention but sufficient for growth (e.g., NO3 10–20 ppm, PO4 1–2 ppm).
- Potassium (K): Important for overall plant health and preventing holes in leaves.
Planting and Initial Stage: How to Properly Start Hemianthus Cuba
Proper planting is half the battle. Cuba is sold in bunches or in pots (In-Vitro).
Preparation and Division
Before planting, the plant needs to be divided as much as possible. If you plant large bunches, they won’t root quickly, and the lower parts will rot. Cuba should be divided into very small clusters.
- Cluster Size: Ideally, 1–3 stems together.
- Tool: Be sure to use long, thin aquascaping tweezers.
Planting Technique
Cuba is planted very densely to minimize the time required for the carpet to close.
- Make a small indentation in the substrate with tweezers.
- Place the Cuba cluster into the indentation, ensuring the root part (even if it’s just the base of the stem) is fully submerged.
- The distance between clusters should be no more than 1–2 cm. The denser the planting, the faster the carpet will close.
Dry Start Method (DSM)
To create an ideal carpet, many experts recommend the Dry Start Method. In this case, Cuba is planted in a moist, nutrient-rich substrate without water, and the aquarium is covered with plastic wrap to maintain 90–100% humidity. Under these conditions, the plant receives unlimited CO2 from the air and forms an ideal carpet in 4–8 weeks, after which the aquarium is slowly filled with water.
Problems and Solutions: Fight for a Healthy Carpet!
Even in high-tech aquariums, problems can arise that require quick action.
1. Carpet Detaching from Substrate
This often happens due to vigorous bubbling (pearling) or the activity of digging fish (e.g., Corydoras, if they are too large). Solution: Immediately secure detached areas and check if the initial planting was deep enough.
2. Yellowing or Whitening of Leaves (Chlorosis)
This usually indicates a deficiency in micronutrients, most often iron (Fe). Solution: Increase the dosage of micronutrients and ensure the pH is not too high, as alkaline water hinders iron absorption.
3. Stem Elongation (Etiolation)
A sign of insufficient light. Cuba grows upwards, trying to “reach” the source. Solution: Increase light intensity (PAR) or lower the light fixture closer to the water.
4. Algae
The most common problem. Cuba surrounded by hair algae or black beard algae (BBA) will not grow. Algae are almost always a consequence of imbalance:
- Unstable CO2: The most frequent cause. Ensure a stable concentration of 30 ppm.
- Excess Light Without Sufficient CO2: Reduce light intensity until CO2 supply is stabilized.
- Nutrient Imbalance: Regular water changes and strict adherence to the fertilizer dosing protocol.
5. Trimming
When the carpet becomes too dense (over 2–3 cm), the lower layers begin to die off due to lack of light and circulation. Trimming Cuba should be regular and aggressive to stimulate lateral branching and maintain density.
Trimming Technique: Cut off the top 50% of the carpet’s thickness with sharp curved scissors every 2–4 weeks. After trimming, be sure to collect all debris and perform a water change.
FAQ: Answers to Frequently Asked Questions About Hemianthus Cuba
Can Cuba grow without CO2?
Hemianthus callitrichoides ‘Cuba’ can survive without additional CO2 supply, but it will not be able to form a dense carpet. Growth will be extremely slow, the plant will be small, and it will likely lose the competition to algae. For an ideal carpet, CO2 is mandatory.
What fish are compatible with Cuba?
Only small, peaceful species that do not dig in the substrate are compatible. Small tetras (e.g., Neons, *Paracheirodon innesi*), Rasboras, shrimp (e.g., Cherry Shrimp, *Neocaridina davidi*), and small Otocinclus (*Otocinclus* sp.) are ideal. Large catfish and goldfish should be avoided.
How fast does Hemianthus Cuba grow?
Under ideal conditions (30 ppm CO2, high light, complete nutrition), Cuba can double its biomass every 1–2 weeks. A carpet planted with 1–2 cm spacing can close in 4–6 weeks.
Which is better: Cuba or Monte Carlo?
Monte Carlo (*Micranthemum tweediei* ‘Monte Carlo’) is often used as a less demanding alternative. Monte Carlo tolerates medium light better and can grow without CO2, albeit slowly. Cuba (*H. callitrichoides*) requires higher light and CO2 but forms a smaller, more delicate, and lower carpet.
Interesting Facts About Hemianthus Cuba
- Smallest: Cuba holds the title of the smallest stem plant used in aquascaping.
- Discovery: The plant was discovered by Danish botanist Holger Windeløv in 2004, making it relatively “young” in the aquarium industry.
- Pearling: With an ideal balance of light and CO2, Cuba exhibits intense “pearling” (releasing oxygen in the form of bubbles), which is a sign of maximum photosynthetic efficiency. It sometimes looks like the carpet is covered in dew or tiny pearls.
- Use in Paludariums: Due to its ability to grow in emersed form, Cuba is often used to green the shorelines in paludariums and terrariums, where it resembles a dense miniature moss.