The Mystery of Algae

  There have been a few threads on algae on this board and in the other 'parish.' And there is a lot of confusion I think, plimarily because we see algae as something we need to get rid of. Rid of because it blocks our view of the koi in the unicellular form and looks unsightly in the filament form on the walls of the pond.
   And we have many names for it- green water, pea soup,blanket weed,hair algae and string algae. And then there is that short green algae.
Pretty hard to know how to treat or not treat these species based on their local and common names?
   The algae we are interested in are the common ones we see. But what are those? There are 5500 species of green algae that can live in freshwater! Let's get a handle on the group and apply our common names to them.
   We have the cyanobacteria- not really algae at all but unicellular or segmented bacteria type algae. This is a very wide group including the famous spirulina! The flat sheet type is what we call slime algae. The filamentous form is Hormogoneae.
   The brown algae we see is actually not of the brown algae group but from the group know as Bacillariariophta to include brown and golden diatoms.
And finally we have the true green algae that have segmented short forms and "hairly forms."

  The only true way to separate the cyanobacteria filamentous forms from the true green algae forms is under a microscope where the nucleus of each cell can be examined for a membrane present/or absent around each nucleus.
   Once the species has been identified, then control can be effected. True hair algae for instance can be controlled by reducing alkalinity.Diatoms can be shifted to true green algae by the regulation of silica in the water. And blanket weed can be curtailed with higher ORP and phosphorous reduction.
   At the end of the day, a good biofilter, a reduction in certain nutrients and high ORP will starvemost species although it is perfectly normal to see seasonal blooms of both free swimming and fixed forms.

  Algae is not so mysterious in terms of content and needs. It needs light. It needs carbon, nitrogen and phosphorus. Algae will then use the light to manufacture complex carbohydrates. So photosynthesis creates this “fuel” and the cells’ respiration uses it.
   So each cell is by dry weight 50% - 56% carbon, 4-6% nitrogen and .08-1.5% phosphorus. Also found in the cell in various amounts are calcium, sodium, potassium, sulphur, chlorine and many trace elements (important metal as a limiting factor – iron).
   The nature of the algal cell is to “store” these materials beyond it’s own immediate metabolic need. This is called its luxury capacity. This guarantees survival when one or more of the nutrients is used up or is diluted in a water change.
   So where do these nutrients come from? Carbon- from organic decay and carbon dioxide. Nitrogen- from nitrate, nitrite and especially ammonium. The aggressive undesirable forms can also remove nitrogen from the atmosphere. And phosphorus - from water source, decay and koi foods. Phosphorus is highly sought after and although small in percentages of dry weight within the cell, is actively stored in the cell.
   Light is also a stimulus and a must for algae. The intensity and duration being key for exponential growth. Each group has a compensation point. That is, a level of light that allows for oxygen production resulting from photosynthesis to sufficient for production of carbon dioxide during respiration.
   Temperature is also relevant. Optimum growth occurring between 20-25C (68-77F) for most species. This is of course, why algae blooms are seasonal in nature.
   The regulation of various species is based then upon all of these parameters. If nutrients are freely available in unlimited supply, it is the faster growing species that will out compete the slower growing forms. We see this for instance when string forms or free floating cells out grow and over grow the more desirable green algae forms in early spring and hot summer periods.
   It is when our systems favor undesirable forms that things get out of hand. High alkalinity for instance favors cyanobacteria growth in an unrestricted way. In fact, scientists have found that cyanobacteria has an affinity for higher alkalinity and calcium. Very warm water stimulates the growth of the blue green and aggressive string algae. And some koi foods are loaded with phosphorus. Some well water contains lots of iron and nitrates. And of course an inadequate filter will supply ammonium to hungry algae. Lots of things to look out for and lots of variables.
   Like heterotrophic bacterial blooms, runaway growth of blue green algae forms and undesirable green algae forms will occur when water is not balanced or is too nutrient rich.
   Algae can be a very desirable component of an outdoor pond, providing vitamins, trace elements and nutrition to our koi in the best and freshest of forms. It can assist the biofilter and remove many undesirable things from the water. In a word -it can ‘condition ‘ water. It can add vitamins and oxygen directly to the water and it can out complete undesirable bacteria species and other microbes and fungi by robbing them of nutrient and growth sites- all good!
   And as with bacteria, a balance of species is best with the most desirable forms dominating. This would require a modestly ‘nutrient rich’ environment with a high ORP reading. This is the same environment in which the best wild type biofilm grows and koi seem to be at their very best. Neutral “ish” pH environment, always oxygen saturated for corresponding temperature, ORP above a minimum of 270Mv and soft to only moderately hard water, is the type of environment we should all strive for. In this setting the biology, including the algal forms, will usually fall in line.