According to the 2012 stats found in the following link
http://www.emwd.org/home/showdocument?id=6283 it looks like the average chloramine residuals from the Mills plant (that supplies Menifee) were 1.3 ppm chloramine. They show a range of <0.2 - 3.2, so assume that during periods of high rain fall, or anything else that affects the organic levels in your area, the level of chloramine could be higher than the average of 1.3. Personally, I would assume 2 ppm year round to be on the safe side, which means that you can go by this: Chloramine: use 5 g (1 tsp.*) to each 1250 L (300 gallons*) of tap water (removes 4 ppm).
Now cut those values in half, as you aren't treating for 4 ppm, but will be treating for 2 ppm. So one teaspoon will treat 600+ gallons in total. Go to the local dollar store and get a set of measuring spoons, then crunch some numbers. 1/2 tsp treat approx 300 gallons, 1/4 tsp treats approx 150 gallons, 1/8 tsp treats approx 75 gallons, etc.
That should set you on the right path.