What is the watts per gallon rule?

There are different variations on this, but what I like to follow is: 

This rule is based on the average lumen output, (brightness) of standard fluorescent light bulb. For more on lighting read: Choosing Your Lighting by Robert Paul H.

What is a substrate?

The substrate is your gravel or rooting medium for the plants. It is important to provide a medium that can both store nutrients and be a source of nutrients for your plants. There are several different approaches to doing this. There are additives made for the aquarium to add to your gravel to provide iron and other essential elements, and more complicated do it yourself recipes that include the use of soils, clays, peat, vermiculite or even clay kitty litter. The term laterite is often used in discussions about substrates. Laterite is an ancient soil made from decaying rocks and weathered by tropical heat and rain. The process has stripped the soil of all nutrients other than oxidized iron, which can be highly concentrated. Land plants can not grow in this type of soil, but in tropical Asia laterite soil run offs are found in waterways providing the iron that aquatic plants need to grow. According to Dupla, a company who first commercialized the use of laterite in the aquarium, there are several grades of laterite, not all of which are beneficial to the aquarium. In fact some can cause harm. In non tropical climates in today's world, ancient laterite rocks, (not laterite soil) can be found, such as areas of the USA. Dupla, who claims to have the only true tested laterite, however there are several other brands available. The term clay and laterite are often confused. They are not one and the same, however many substrate materials are either laterite or clay based. Both for all practical purposes provide the same thing: a source of iron and the ability to hold nutrients it absorbs from the water.

Clay gravel is another alternative to laterite. This should be used without adding laterite to it. It is advisable to learn more about what nutrients plants need, and what's involved in a substrate method before getting involved in it. Do not blindly mix different approaches together without understanding the consequences. For example, too much organic material, peat or top soil, can cause severe problems. Kitty litter can alter your pH.

Adding garden fertilizers to an aquarium will dramatically raise the nitrate level, since the chief ingredient is nitrogen, putting your fish at risk and at the very least causing a huge algae outbreak.

Not all plants need to draw nutrients from the substrate. Floating plants obviously do not, as well as plants that anchor to rocks or wood. Most plants take nourishment from both the roots and the leaves, but some rely more heavily on root feeding than taking it from the water. Read more HERE

Do I need CO2 in order to grow plants?

Yes and no. All plants will benefit from adding CO2. Some plants are nearly impossible to grow without it, and the brighter your light the more of a demand there is for CO2. In general, most stem plants require bright light therefore have more of a need for CO2. There are some exceptions. Hygrophila polysperma and Egeria najas seem to hold up better under lower light and CO2 conditions. 

Slow growing plants such as Anubias, ferns, and Cryptocorynes, which instead of having stems grow from a crown or rhizome will grow faster and more robust with added CO2, but can remain healthy and slow growing without it. Read more HERE

What type of plant tank?

What do you want to achieve? In most cases the lights that come standard with an aquarium are not sufficient to grow most any plants. It is not the brand of the bulb that makes a difference, but not enough light bulbs. You have two basic choices: reaching the minimal level to grow easy and slow growing plants or reaching the level that will enable you to grow most anything. Lighting is the first most important factor.

Low tech tanks use minimal lighting, no added CO2 or instead Do it yourself CO2 . Choice of plants is more limited

Higher tech tanks use lighting intensive enough to meet the needs of any aquatic plant, pressurized CO2 systems, and sometimes additional equipment for more optimal results. The difference is simply a wider choice of plants, namely hundreds of stem or "bunch" plants

Often times cost is the biggest factor when determining the type of plant tank or approach. Lighting can be the most expensive component.  It can be as simple as adding a dual fluorescent strip fixture, or a power compact fixture, or for larger tanks a much more elaborate lighting system.

Artistic arrangements can be done with either a low tech or high tech approach as long as the growing requirements of the plants used are being met.

For more details on substrates, lighting, fertilization, CO2, Biotopes, and more, please visit the Library !!