Re: Aquatic Plants Digest V1 #262

 Hello Eric

Just a few comments on the pH electrode. It will probably prove to be 
impossible to find an electrode that does not have a "Calomel" reference 
cell in it (that is the bit with the silver). It is used to give the 
signal that allows the electrode to work. The electrodes use a special 
glass that only allows H+ ions accross and this is reduced by the 
platinum elctrode in the probe itself, the difference between the 
reference elcetrode and the platinum one is what gives rise to the value 
on your meter. 

In one pf my planted tanks I noted a .6-.7 pH shift from the time that 
the lights came on till they went off. This was in my pre CO2 days.

Peter Hughes

Sunny warm Canberra Australia.