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Pond Algae Control - by Carl Strohmeyer


I will discus two primary algae problems; green water (or free floating algae) and attached algae such as common hair algae (also known as blanket algae).

First of all water chemistry is important for both types of algae. A pH between 7.0 and 8.0 is important and even more important is a
GH between 100 and 300 and a KH between 50 and 150 . This will in aid in maintaining a healthy Redox Potential. Good circulation and filtration are also important (please see my full pond article for more about this: “A Clear Pond”; Pond Information).
Finally a well
Cycled pond where ammonia is 0, nitrites are 0, nitrates are less than 50 ppm, and phosphates near 0 is very important to algae control.


Green water is basically single cell algae that is usually too fine to be filtered out by most common pond filters (sometimes Diatom filters can achieve this).
Control of green water may involve several parameters and methods or sometimes just one or two.

Here are parameters and methods worthy of note:

*As noted above, a GH between 100 to 300 and a KH between 50 to 150 are important. This effects Electrolyte levels and Redox Potential as well as pH. Water changes, ‘flow through’ circulation, and products such as Wonder Shells can also help (avoid use of Plaster of Paris).

*Decay and Bio Load; If you have a lot of decaying matter in your pond (usually on the bottom, however this can also be in a poorly maintained or designed filter as well), a high bio load (too many fish, fish waste, uneaten food, ECT), these will add to Nitrogenous waste (such as nitrates) which will provide nutrients for algae growth. Lowering your fish count, improving the quality of your Fish food (to lower fish waste due to lower food digestibility due to poor ingredients), and most important lowering the amount of decaying matter in your pond will improve this factor for algae control. Also as per the nitrogen cycle make sure you have a functioning Bio system in your pond (via filtration, veggie filters, ECT).

*UV Sterilization; probably the king of green water control, A properly installed UV Sterilizer with a pond turnover of at least once every three hours and a flow rate through the UV of no faster than 40 gph per watt is very effective for the control of green water. The UV Sterilizer will also aid in Redox Potential which further helps in green water control. Please read this article for much more information about UV Sterilization: Ultra-violet Sterilization; How UV Sterilization works

*Barley Pellets; this is a so-so method in my opinion for green water control, however this can work or aid in green water control especially in milder cases or in conjunction with other methods and parameter controls. Barley pellets or even extract are more effective than straw due to the higher concentration of Iodine which has been shown to be the effective ingredient in this method.

*Blue Dyes; Some inert Blue dyes can be used like a sunblock, these work to prevent light penetration into the pond which slows or inhibits algae growth. Methylene Blue may be used in a pinch, however even though it works even better than ordinary blue dyes for algae growth (due many of Methylene Blues medicinal properties) it also will destroy beneficial nitrifying bacteria and is very harsh on aquatic plants with long term use.

*Veggie Filter (plant filter); these remove many nutrients that algae need and are one of my more successful methods for pond green water and algae control (even without UV Sterilization). Please read this article for more information and methods for veggies filters: Pond Veggie (plant) filters

*Algaecides; I do not recommend these as these are only a quick fix that often makes the situation worse in the long term. As algae are killed, they then die and add to the bio load which will then add more nutrients and pollutants to the water column which will further exasperate the algae problem.

HAIR ALGAE (Blanket Weed);

*Again as noted above, a GH between 100 to 300 and a KH between 50 to 150 are important.

*Barley Pellets; I have found this more effective for control of blanket weed than green water. Beer has also been used for blanket weed control.
Barley pellets or even extract are more effective than straw due to the higher concentration of
Iodine which has been shown to be the effective ingredient in this method.

*Decay and Bio Load; Basically the same as the previous description for green water control.

*Veggie Filter (plant filter); these remove many nutrients that algae need. I have not had quite as good of success with blanket weed control as with green water control, however they still aid substantially when used in conjunction with other sound pond maintenance procedures.

*Flow through filtration; adding an over flow to remove water while a small amount of water is constantly added will control nutrient levels and aid in Redox and mineral replenishment (depending on the water parameters of the new added water).

*Manual removal; this kind of goes without saying however since a pond is a living organism unlike a swimming pool, algae is going to be present in some form no matter what you do and removal by hand or implement is to be expected.

For the more complete article, please visit this link: http://www.americanaquariumproducts.com/PondAlgae.html


Professional aquarium maintenance experience since 1978 as the owner of one of the larger aquarium maintenance companies in LA, CA.

I have been in the hobby since 1969.



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