Although almost no aquarist knows this (athough every marine biologist does), algae produces all the vitamins and amino acids in the ocean that corals need to grow. Yes these are the same vitamins and amino acids that reefers buy and dose to their tanks. How do you think the vitamins and amino acids got in the ocean in the first place? Algae also produces a carbon source to feed the nitrate-and-phosphate-reducing bacteria (in addition to the algae consuming nitrate and phosphate itself). Yes this is the same carbon that many aquarists buy and add to their tanks. In particular, algae produce:

Vitamins:

Vitamin A
Vitamin E
Vitamin B6
Beta Carotene
Riboflavin
Thiamine
Biotin
Ascorbate (breaks chloramines into chlorine+ammonia)
N5-Methyltetrahydrofolate
Other tetrahydrofolate polyglutamates
Oxidized folate monoglutamates
Nicotinate
Pantothenate


Amino Acids:

Alanine
Aspartic acid
Leucine
Valine
Tyrosine
Phenylalanine
Methionine
Aspartate
Glutamate
Serine
Proline


Carbohydrates (sugars):

Galactose
Glucose
Maltose
Xylose



Misc:

Glycolic Acid
Citric Acid (breaks chloramines into chlorine+ammonia)
Nucleic Acid derivatives
Polypeptides
Proteins
Enzymes
Lipids


Studies:

Production of Vitamin B-12, Thiamin, and Biotin by Phytoplankton. Journal of Phycology, Dec 1970:
http://onlinelibrary.wiley.com/doi/10.1 ... x/abstract

Secretion Of Vitamins and Amino Acids Into The Environment By Ochromanas Danica. Journal of Phycology, Sept 1971 (Phycology is the study of algae):
http://onlinelibrary.wiley.com/doi/10.1 ... x/abstract

Qualitative Assay of Dissolved Amino Acids and Sugars Excreted by Chlamydomanas Reinhardtii (chlorophyceae) and Euglena Gracilis (Euglenophyceae), Jounrnal of Phycology, Dec 1978:
http://onlinelibrary.wiley.com/doi/10.1 ... x/abstract