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Algae releases CO2 (carbon dioxide) constantly due to respiration. However, during the day it is consuming more CO2 for photosynthesis than is it releasing from respiration. Therefore, the CO2 level drops throughout the day to a minimum in mid-afternoon. Since CO2 is a weak acid, the pH goes up in afternoon.
All industrial fish production ponds operate with an algae bloom (green water). The first thing to be careful of is low dissolved oxygen at night. That algae respiration which is producing CO2 is also consuming dissolved oxygen. During the day, there is more oxygen produced through photosynthesis than is consumed by respiration so the oxygen will also be very high in mid-afternoon. When the sun goes down and photosynthesis stops, the respiration continues and dissolved oxygen will begin to fall . The lowest oxygen concentration will be found about dawn.
You need to be especially vigilant when the weather changes and you get heavy cloud cover after a period of bright sun. Under these conditions, algae respiration continues as normal but photosynthesis is reduced so the dissolved oxygen at dawn will be lower than usual. On occasion, the algae bloom will ''crash'' and disappear almost overnight. This is when you have to really be on your toes. The decaying algae will use even more oxygen and most of the nitrogen which was ''stored'' in the algae cells will be released back into the water as ammonia.
If you have aeration to counteract the oxygen depletion at night, then you do not normally have to worry about algae - unless its an ornamental pond where you want to see the fish. Despite the dogma you hear on koi boards, the pH swing does no harm in production ponds.
Despite the pH swing and oxygen swing, algae can add a certain amount of stability to the pond with respect to ammonia and other nitrogenous waste. The algae will respond to an increase in nitrogen by becoming denser. When nitrogen is used up, algae concentrations will slowly decline.
The only safe way to control algae is by exchanging water - and this does not work very well. If you quit feeding long enough, you can starve the algae, but you starve the fish and sacrifice growth.
Algae (green water) is the base of a food chain which is producing free food and providing magical sources of nutrition for the fish. When production is the primary goal, you try to promote a healthy level of green water - not eliminate it.
All of the above applies to suspended single cell algae which comprise green water. However, filamentous algae (string algae, hair algae, macrophytes, whatever you want to call it) behaves in much the same way. One difference is that you cannot flush filamentous algae out of the pond with water exchange, but you can remove it manually. Filamentous algae is not as good at promoting that natural food chain, but koi will directly eat many types of filamentous algae.
Always remember, what goes into the pond must eventually come back out of the pond.
-steveh opkins
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09-30-2005
What would happen if he stops feeding and ammonia spike or what? Why is it that when I have a algae bloom and I put plenty of plants in the pond the bloom will go away, is it because the plants are eating up the fish poop and in turn the water clears. I do understand what you are saying about slowly reducing feeding and this will stop the bloom, but what is the problem here?
Just try some other brain storms and leave the fighting to the insane. Do you remember the Mayflies, you were right of course
but we made it through it ok.
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