re:pH probe

if your reading when you have the probe in a calibration solution isn't 
'dithering' then the jumping readings may be related to the rate at which you 
injecting CO2 causing the system to over and undershoot the set point due to 
the time necessary for a given amount of co2 to enter the water and to mix 
One way to test this would be to try setting the needle valve (I assume these 
automatic systems have a way to control flow) to a lower flow rate or

 you could just take the system off automatic and adjust the flow manually to 
maintain the pH you want at the end of the day when the plants are/have 
consumed the max and then go back to automatic since that flow rate should be 
about the max you'd need.  Can you tell if the system is cycling fairly 
rapidly off and on?  Just gradually reducing the flow rate should lead to 
longer 'on' times and a decrease in the amount of 'dither' if this is the 

My setup is manual so this isn't experience, just a guess. (BTW, my nupro S 
series valve has to be almost at closed with 10PSI to get down to 1 bubble per
second...did I mess up the valve or is there a finer control available out 
there somewhere?...haven't built my controller yet).

Jim Morehouse
aljem3 at attme_att.com