I'm pretty impressed with Spirulina.
Spirulina is an algae (actually cyanobacteria) with an amazing nutrient profile (see below), which can be farmed with relatively minimal effort once you've climbed the learning curve.
Although farming it under its own ideal conditions does require energy investment to keep the culture at ideal temperature, and loaded up with plenty of light, Spirulina will grow -- just not as efficiently -- under whatever natural Sunlight conditions it receives, and can exist within a reasonable temperature range. It will die if it gets too cold (< ~45'F) or too hot (> ~108'F), but beyond that, growth suffers. See chart:
Believed to have been a staple for the Aztecs, recorded history dating to the Conquistadors confirms that spirulina cakes were regularly sold as far back as the 16th century. One of the most elaborate explanations we have from this time comes from Cortez in his book, “Conquest of Mexico.”
“They make it into cakes like bricks, which they sell, not only in the market (of Tenochtitlan) but carry it to others outside the city, and far off. They eat this as we eat cheese, and it has rather a salty taste, which is delicious with chilmolli (a pungent sauce). They say that so many birds come to the lake for this food, that often in winter some parts are covered with them.” 
Referred to as “Tecuitlatl,” spirulina was a primary source of protein for the Aztecs for several hundred years and Lake Texcoco remains an abundant fountainhead of this Superfood still today.
Nutrition / Uses
I've placed a detailed article here: Spirulina Nutrition PDF.
As well, via Dr. Axe, here are some noteworthy uses and benefits of Spirulina:
Eliminates Candida / Immune-boosting
Several animal studies have shown that it’s an effective anti-microbial agent, particularly for candida.  
Specifically, spirulina benefits have been shown to promote the growth of healthy bacterial flora in the intestines, which in turn inhibits Candida from thriving. Additionally, the immune-strengthening properties of spirulina will help the body eliminate Candida cells.
Detoxes Heavy Metals (especially Arsenic)
After giving 24 patients affected by chronic arsenic poisoning spirulina extract (250 mg) plus zinc (2 mg) twice daily, they compared the results with 17 patients who took a placebo and found that the spirulina-zinc combination worked wonderfully. Ultimately, the participants experienced a 47% decrease of arsenic in their body!
According to the University of Maryland Medical Center, “A number of animal and test tube studies suggest that spirulina increases production of antibodies, infection-fighting proteins, and other cells that improve immunity and help ward off infection and chronic illnesses such as cancer.” 
This doesn’t come as a surprise as more than 70 peer-reviewed articles have been published in the scientific literature evaluating spirulina’s ability to effect cancer cells! 
In an article published this past April, Czech Republic scientists pointed out that, in addition to its ability to control blood cholesterol levels, “Spirulina is also rich in tetrapyrrolic compounds closely related to bilirubin molecule, a potent antioxidant and anti-proliferative agent.” 
When tested on human pancreatic cells, these researchers discovered that, “Compared to untreated cells, experimental therapeutics significantly decreased proliferation of human pancreatic cancer cell lines in vitro in a dose-dependent manner.” Essentially, this proves that consuming spirulina can help prevent developing various cancers!
Lowers Blood Pressure
Phycocyanin is a pigment found in the spirulina that scientists have discovered possesses antihypertensive effects (it lowers blood pressure). Japanese researchers claim that this is because consuming the blue-green algae reverses endothelial dysfunction in metabolic syndrome.
I find this extremely promising for Americans because metabolic syndrome has rapidly become one of the main causes of preventable disease today, as it raises one’s risk of developing heart disease, diabetes and stroke.
Reduces "bad" Cholesterol
Along those same lines, spirulina benefits have also been shown to prevent atherosclerosis and reduce elevated blood cholesterol levels.
A recent animal study published in The Journal of Nutritional Science and Vitaminology took rabbits, fed them a high cholesterol diet (HCD) containing 0.5% cholesterol for four weeks, and then fed them a HCD with 1% or 5% spirulina for an additional eight weeks. 
After the eight-week trial was complete, LDL levels decreased by 26% in the group eating 1% of spirulina and 41% in the group eating 5% spirulina, which heavily suggests that the more we eat the more benefits we will receive! Serum triglycerides and total cholesterol were also significantly reduced.
When you look at the chemical composition of spirulina, it’s no wonder that people who regularly consume it have an abundance of energy. Dr. Oz recommends combining 1 tsp spirulina powder with 12 oz lime juice and freezing the mixture in ice cube trays for a healthy boost.
According to Dr. Oz, spirulina and lime enhance energy performance because they unlock sugar from our cells and, when frozen, the cold from the ice boosts metabolic energy while giving our bodies a “wake-up call.”
Obtaining a Culture
There are a handful of reputable sources. I have sourced spirulina platensis from, and can personally recommend:
- Algae Research Supply -- available through Amazon
- Dr. Aaron Baum (former NASA)'s AlgaeLab.org; his book is authoritative and can dispel much confusion you might have after noticing the CONFLICTING information on the web
Building a Medium: Recipe
See Spirulina Medium.
Once your culture has grown into its medium and the pH has stabilized above 10, you are ready to harvest.
Harvesting requires a 50-micron screen, which will catch the individual algae cells, allowing the nutrient solution through to be replaced into the culture to grow more!
Feeding your Culture
As you harvest, you will need to feed your culture to replace the nutrients removed by virtue of harvesting algae.
The nutrient recipe is here: Spirulina Nutrient Mix.