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pH Controllers

I forgot to mention another recently noticed benefit of using a pH
controller.  You can actually measure photosynthetic activity in the
time it takes the pH to drift up from setpoint; in my case 0.1 pH units
from setpoint.  This is due to the plants taking CO2 out of solution as
well as some loss at the air-water interface.

So when the lights come on, it may take 20 to 30 minutes for the pH to
drift 0.1 pH units, but after an hour or so this time starts to decrease
(all I do is listen for the clicks the controller makes when it turns on
and off).  If everything remains constant, i.e., lights, water
circulation, plant mass, etc., then the decrease in the time it takes
for the pH to drift up can be taken as a measure of photosynthetic
activity.  For example, at 8 hours after lights on I've measured 17
minutes, then 13 minutes, then 10 minutes, all after consecutive
additions of CO2 by the controller.  The point is that this data can be
used as a gauge in determining how well your plants are
photosynthesizing.  I've even noticed that after heavy pruning,  the
measured interval increases.

Just thought I'd mention another benefit a pH controller can have.