Algae is a very efficient low-tier fertilizer for Trays. It can be found on Bog planets in great quantities, and will appear on almost any surface block (similar to ores) when under the Bio Rain weather. It can also be grown from Algae Pod seeds. It is also produced by Water Generator (in small quantities).
Algae is notable for growing extremely fast. It is very convenient to grow Algae Pod in Trays and then use the produced Algae as fertilizer for other plants. Algae can even be used as fertilizer for growing itself. It also decreases the amount of liquids that is consumed by Trays.
While its bonuses are very decent for the early game, even the most basic crafted Fertilizer will provide higher output.