If you do the math then you'll find that over time the Hanna colorimeter quickly approaches the prices of the Merck kit because the Hanna refills are 2/3rds the price of the Merck ($21/100 vs. $30/100). I didn't factor in batteries, however. So if you're checking your tank and GFO reactor effluent levels regularly then you might as well get the colorimeter.
jdieck: you rock, have you published the results of your GFO testing anywhere? I didn't find it on your site...
jdieck: you rock, have you published the results of your GFO testing anywhere? I didn't find it on your site...