I'm not a big fan of Hagen... A different test kit with units in ppm, dkh, or meq/L would make this a little easier. Also, make sure that your test kit isnt past its expiration date. Are you sure the test kit didnt mean ppm? If its 80ppm then your alkalinity would be 4.48dkh which is really low. You can boost it with baking soda using this online calculator
http://reef.diesyst.com/chemcalc/chemcalc.html
"Alkalinity is a measure of the amount of acid necessary to reduce water's pH to the point where all carbonate and bicarbonate have been converted into carbonic acid (about pH 4.2 in seawater). In seawater, bicarbonate and carbonate provide nearly all of the alkalinity. Consequently, reef aquarists can use it as a surrogate measure for bicarbonate and carbonate which are taken up by calcifying organisms (Figure 1). The units of alkalinity can be meq/L (milliequivalents per liter), dKH (degrees of carbonate hardness), or ppm (meaning ppm of calcium carbonate equivalents). One meq/L = 2.8 dKH = 50 ppm CaCO3 equivalents. Seawater has an alkalinity of about 2.5 meq/L = 7 dKH = 125 ppm CaCO3 equivalents."
From:
http://www.reefkeeping.com/issues/2005-08/rhf/index.php