Alkalinity demand can be very variable for sure! FIRst you must understand that ALK is your buffer it maintains the pH of the tank. Second bacteria produce acid which eats your buffer up! The more you feed the tank the more bacteria consume the food and produce acid. Also, if something in your tank dies (god forbid) it will decimate your alkalinity. So you must pay attention to your livestock. When establishing a baseline you need 1) everything in the tank thriving and 2) you need to feed the exact same food each day for a week or so while testing how much your alkalinity is dropping. Then if your parameters are all stable you can go and calculate exactly how much alkalinity you need to add to your tank for a 3-4 day period.
For example start your alkalinity at 9.5 and let it drop for a week or so (I wouldnt let it go below 7 just to be safe.) when it hits 7 go to BRS alkalinity calculator and calculate how much carbonate is needed to increase your alkalinity from 7 back to 9.5 based on how many gallons your aquarium is. set up your dosing pump to add that amount over the allotted time span and your are in business