If the CH is rising with no calcium being added, then it might be coming from the plaster.
Note that there can be CH in the fill water, and depending on where you live, it can be a substantial amount. Easy to measure with your kit.
So how much would you use in a say, a week?
Short version: dunno.
I suppose I should/could figure that out, but I don't actually know. My IntellipH calculates the hourly dose based on a user-adjustable setting. But that setting is 0-100, so it's not in ounces of acid. (Because the IpH controller doesn't know what percentage of acid is in its hopper.)
I've never bothered to figure it out because it doesn't really matter for my MO. I adjust the 0-100 based on the pH level in the pool, and I base what pH I want in the pool based on CSI, which fluctuates throughout the year (primarily because of water temperature). If it helps, I run about pH7.5 in the heat of summer, and about 8.0+ in the dead of winter.
I load up the IpH with 31% muriatic diluted 1:1 with water. It seems I've barely used any this winter, and maybe go though about five or six gallons a year total. Again, I don't really keep track. My pool tells me what to do, and I just do it!
I've been tempted to pull the injector to measure exactly how much acid it dispenses per minute, but I'd question the result. One, I change the setting throughout the year, and two, I'm not sure the amount I'd measure would be the same as when the injector is in place, because of the back-pressure of the water in the plumbing. And since the actual amount dispensed would still have no bearing on my MO, I've just never been inspired enough to find out.
I think the manual indicates the dispensing rate, but, again, because my rate changes throughout the year, it would be quite a task to figure it all out, and even if I did it would be of no use to me.
More to the point, acid consumption is based on a handful of factors, primarily what your plaster is doing, the pool's annual average water temp and the chemistry of your fill water. So even if I could give you a number, unless you lived next-door with a pool that had a size, shape and finish exactly like mine, installed when mine was, it wouldn't tell you anything useful.