[APD] Re: theory behind algae control

["Roeland Grommen" <roeland_grommen at UGent.be>]

Thomas Barr wrote:

> Algae can use dissolved organic forms of P and N, (DON, DOP) wereas most
> submersed plants cannot. Large water changes will remove the organic
> fraction that builds up.
> But...... a healthy well balanced bacterial colony will help reduce the
> DON/DOP and reminerilize the decayed matter. This takes perhaps 3-4 weeks
> to occur. Once this occurs, the tank can get away with less water changes,
> but it still helps to have the large water changes to keep anything from
> running out(nutrients).

This is very interesting! Having a filter in a planted tank does make sense
after all? Maybe not for nitrification, but for dissolved organic matter
removal. There seems to be quite a lack of knowledge in scientific
literature about the role of heterotrophs in aquaria and aquaculture
systems, though. But it seems logic that having a nice and balanced
community of heterotrophs that can degrade organic matter down to very low
concentrations helps higher plants by releasing N, P from their organic
products. From mass balance studies it is known that one can remove
substantial amounts of P by removing suspended solids in aquaculture
systems.

But to come back to the original question: the idea would be, like Roger
Miller says, to select a window of conditions. Unther those conditions
plants are better competitors than algae. 'Clean' water, free of dissolved
organic matter seems to be part of the solution. Maybe also that is logic if
you compare an aquarium with the lakes Tom mentioned: fish density and waste
production per m3 will always be higher in an aquarium than in a lake.

Roeland


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