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Re: Question for George Booth

Very frequently I see suggestions of target Co2 concentrations of 15 mgl.
for planted aquaria. My experience has shown Co2 concentrations to be
constantly changing rather than a fixed value. In my tank just before the
lights come on pH is 6.9 at 5.5 KH or 20 mgl. when the day is spent and the
lights go out pH is 7.2 or 10 mgl. At what time of light day does one want
to achieve an ideal 15 mgl?

I have also observed daily pH swings to be a good sign of overall tank health.
For example:
Recently as my tank became nitrate limited it's pH swings began to get
smaller as the plants stopped growing. Then when the blue green algae
appeared both morning and evening pH measurements rose, first one tenth and
then another as the BGs took hold.

Another example:
Three months ago I first set up my tank planting heavily with very sad mail
order plants. Without Co2 supplementation my pH began to drop away from its
initial static 7.6, probably caused by of decomposition of rotten plants.
As the plants began to grow night time pH drops got bigger till one day I
arose to a pH of 6.3 and fish gasping at the surface. Aeration fixed my
temporary low and the daytime pH rise began to grow along with the plants
progress until the tank settled back down to 7.5 - 7.6 pH.

What do you think, are daily pH swings a good diagnostic tool?

Jeff Kropp