Growing Aquatic Plants - Tech Talk 117
When you want to grow freshwater, submerged aquatic plants, you need to keep three water quality parameters in mind: GH, KH and pH. GH is general hardness—an important measurement of calcium and magnesium ions, which are essential for healthy plant growth. KH is carbonate hardness, a measurement of carbonates in the water, which are important because they affect pH stability, especially when CO2 is injected. A KH of 4 to 6 is a good range. The pH level is a measure of the acidity or alkalinity of the water. Some metals essential to plant growth are only available when the pH is below 7. Consult a text such as Aquarium Plants: The Practical Guide to learn the ideal water chemistry for the plants you want to raise.
The substrate is another important element. It is a rooting and anchoring medium, so it should be permeable by the plants' roots and weigh enough to keep plants rooted. The substrate also provides nutrients. Plants may prefer foliar uptake of nutrients, but they do better absorbing nourishment from both the water and the substrate.
Lighting is very important, as plants' growth will be proportional to their ability to photosynthesize. Keep water clear, and lighting, if done indoors, should approximate natural light (sunlight). A good temperature range (Kelvin rating) for indoor lighting is between 5,000K and 10,000K.