On the most basic level, the first thing needed for any of aquatic plants to thrive under water is a nutrient source. There are many routes through which nutrients can reach the plants or be added into a system.

 

The first route that comes to mind is through the substrate; this can be compost capped under the gravel, a quality aquasoil or (in a tank with only gravel) through root tabs which slowly release nutrients directly to roots. Adding nutrients this way benefits Rosettes, stems, carpeting plants and any heavy root feeders the most. 

 

The second route that immediately occurs to me is through the water column. Nutrients in the water column may leech from the substrate and from decaying matter in the system like rotting organics or animal waste. Specialized aquarium liquid fertilisers can also be added to the water in adequate doses to boost water column feeders. Nutrients present in the water column, in truth, are consumed by all plants but are primarily absorbed by faster growing stems, floaters, moss and rhizomatous plants.

 

The complex relationship between aquatic plants and their environment doesn't end there. Plants in an aquarium depend on good lighting. I often use LED floodlights with a minimum of 20 watts; I mainly go for this minimum only when searching for cheap LED floodlights as I have seen many aquarium specific lights with lower wattages that are bright enough to grow plants. It helps a lot to use full spectrum lights which incorporate all the light frequencies in visible light; although they will do a lot better with full spectrum lighting, I have grown aquatic plants with many different types of lights.

 

However high lighting serves no purpose when the dissolved oxygen in the tank is depleted. This part of the process baffled me when I first learned about it.

Although aquatic plants consume CO2 and release O2 during the day as a function of photosynthesis, at night these plants actually consume O2. Lacking the oxygen needed to breathe at night can stunt plant growth and cause algal blooms. Knowing this can help you make educated guesses as to when a water change is necessary as water changes are the most immediate solution to oxygen depletion.

Oxygen levels can also be regulated through surface agitation; the waves and ripples increase the size of the waters surface creating a larger area through which gasses can pass into the water column. Believe it or not this is the actual purpose of bubblers and air stones in aquariums. The air pumped into the water moves too quickly to dissolve effectively; it is the disruption of the surface by the bubbling that actually oxygenates the water.

 

Aquatic plants also use Carbon dioxide within the aquarium. They use it during photosynthesis to create the sugars that fuel their growth. CO2 is a little less of a worry, in my opinion, as there are more sources through which it can be accessed within an aquatic system. CO2 passes from the atmosphere through the waters surface just like oxygen but it can also come from the breakdown of minerals and rock, from the decay of organic matter in the tank and from the respiration of fauna that may live in the system.

It is common practice, however, to inject CO2 into an aquarium using specialised gas systems that can be bought at most pet shops or online. Doing this boosts plant growth and limits algae growth but it can only work if the lighting is bright enough and nutrients abundant enough for the plants to justify using all the extra CO2. I like to imagine that it functions like climbing down a rope from a cliff to reach the ground; the ground being the light (where you're trying to go), the rope being the C02 (the resources you have to get there) and the food you might eat being the fertiliser/nutrients (energy you have to complete the task). If the ground is close enough, then there's no need for more rope. If you haven't got enough rope then you'll just have to stay where you are. If you have no nourishment and you're tired, then you won't have the energy to execute the task despite having the resources; all the elements need to be in balance for the plant to reach its goal.

 

Although this may seem like a lot of intermingling forces to keep in mind, I strongly believe that knowledge fuels discernment and intuition; with this information you will be a step closer to understanding what may be going on with your plants in your system and developing your own method for moving towards creating the scape of your dreams.