[APD] RE: Acidity and nutrient uptake

["Ed Hengel" <ed-hengel at rcn_com>]

Steve

After rereading your email it occurred to me that there is one other
difference between the two tanks that I failed to mentioned.  The one
experiencing the problem has a flourite substrate and has been the less
stable of the two tanks on the automatic RO water changing system since
switching it over from gravel several years ago.

According to the graph at:
http://www.extension.umn.edu/distribution/cropsystems/DC0792.html
 phosphorus availability is at one of it's lowest points at precisely the ph
measured.

You intimated that the rate of aluminum phosphate fixation was dependent
upon having a clay or fine mineral substrate.  Why is that?

I'm sure that the topic of phosphate availability and it's effects on plant
and algae growth have been addressed here before, and if so I apologies for
posing the question to the list again:  If the problem turns out to be
phosphate fixation due to low ph with a clay substrate; does a high
temperature, phosphate deprived environment, favor the growth of algae over
plants?

If not, then the problem might simply be the lack of minerals such as mg,
ca, k, etc. from the failure to replenish them at more regular intervals.
But then the question of why the instability in the clay substrate tank and
not the gravel tank, with the only difference being temperature, would still
persist.

However, if algae can thrive in a phosphorus depleted environment, the lack
of which a result of being fixed in the form of aluminum phosphate due to
those occasional (rather long) periods of low ph coupled with a clay
substrate, it certainly would explain a lot!

Ed


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