OK, I need sot make some clarifications here as I jumped the gun somewhat
First, this is not really clear;
Looks like add 50 % :lol: Reading 100 ppm add 50 ppm = 150 ppm
That is the HACH going to the Hanna. So, from the Hanna to equal the HACH it is subtract 50 % HOWEVER, at what many run their Alk at 180 ppm = 3.6 meq / l = 10 dKH it is more like subtract 25% of Hanna reading. At the HACH 180 and the HANNA 240 mark. Hanna 240 x 25 % = 60 and 240 - 60 = 180.
But there is more here
Dana's link on Alk is not to Randy's link on Alk.
What is Alkalinity
http://www.advancedaquarist.com/2002/2/chemistry
From it:
The precise endpoint of a total alkalinity titration isn't always the same pH, but rather depends a bit on the nature of the sample (both its ionic strength and its alkalinity). For normal seawater, this endpoint is about pH = 4.2. In freshwater it depends strongly on the alkalinity, with an endpoint of pH = 4.5 for an alkalinity of 2.2 meq/L, and pH = 5.2 for an alkalinity of 0.1 meq/L.
Well, the Hach kit was designed for use in fresh water where the pKa of the bicarbonate is much higher than in seawater, and in that situation, it is appropriate. In seawater, however, it is marginal. My tank water took 3.4 meq/L to get down to pH = 5.03, and then an additional 0.4 meq/L to get down to pH 4.00. Consequently, this kit (and others with a similar dye mix) may be missing out on 10% of the alkalinity simply because it isn't titrating low enough. This difference obviously isn't significant to most reef keepers, but is something to keep in mind when doing such things as comparing test kits to standards (in seawater) or to each other.
So now we need to add 10 % to that HACH reading of 180 = 198
Now the Hanna is reading 18 % to high.
HACH = 198
Hanna = 240
240 x 18 % = 43 and 240 - 43 = 198
So, the correction error for the Hanna to get a better true value is :
Hanna - 18 % of reading at ~normal pH and Alk.
This is MY fault for NOT thoroughly reading th article and all that it does and did not involve. I will let Danna know.
Sorry guys