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Re: pH of ~ 8 okay?

Nathan Wittmaier wrote:

> Hullo. I know that pH has been discussed quite a bit, but I was wondering if
> a pH in the range of 7.8 to 8.2 is suitable in general or if certain plants
> would prefer it.

I don't think there's very much of a direct effect of pH on plants. 
Mostly high pH is a problem because it implies low CO2.  Some plants can
do very well under those conditions - Vallisneria comes to mind as a
good example.  If you want to grow plants under low-CO2, high-pH
conditions then I think you have two possible approaches.

With bright artificial light or sunlight a few plants will do very well
using bicarbonate as their carbon source.  You probably will find that
only one or two species of plants will coexist under those conditions,
because there is very intense competition and plants that are less
well-adapted to those conditions will die.

With dim light you can grow a larger variety of slow-growing plants that
can subsist on low CO2 supplies.  Plants grown under low light w/o CO2
generally aren't very robust; they respond poorly to temporarily bad
conditions and they don't recover very well from damage (like pruning or
transplanting).  Plants grow slowly under those conditions, so they
won't do much to control the level of nutrients (nitrate, for instance)
in the water.  Some algaes (BBA comes to mind) grow relatively well
under these conditions.

> According to the local water department, that is the pH out
> of the tap. The little color-comparison pH test kit I have only goes up to
> 7.4, and my reading from tank water seems to be above that. I don't
> supplement with CO2 and don't plan to. Should I make efforts to adjust or
> just not worry about it?

Don't use chemical additions to adjust the pH of your water -- they tend
to cause more problems then they solve.  You can mix your water with RO
or distilled water to get a lower pH, and reduce aeration or surface
turbulence to retain more CO2.

Roger Miller