From McMurray for a comparible powder they suggest 1 tsp to a gallon maintenance or 2 tsp a gallon during outbreak, in the text but slightly different dosage on the sticker they stick to the bag... Looks like dosage is pretty forgivable...
http://www.mcmurrayhatchery.com/sulfadimethox_albon_.html
Grams are a measurement of mass a teaspoon is a measurement of volume... Yes a teaspoon of WATER is about 5 grams, and that conversion of volume to mass ends there, unless the substance being converted has the same density as water...
If the medication is a liquid it's probably still close to...