Quote Originally Posted by FrankToil View Post
I guess my biggest concern is that the FC is staying down after a fair bit of granular hypochlorite and bleach, even though the CYA is about 25 or so.
CYA = 25 is not high enough to prevent significant chlorine loss during a sunny day. Also, algae -- even when it's not a full 'bloom' -- introduces a substantial chlorine demand, so you need to eradicate it.

My basic questions are two: First, that kit is indicating a nonzero level of Br.
All the pool chlorine tests available are actually either free halogen tests, or else more generalized oxidizer tests. When your kit is showing a Br value, it's simply showing a chlorine value on a different scale. There's actually no deck-side method to distinguish a 1 ppm free chlorine residual from a 2.25 ppm bromine residual. (Reaction to the test reagent is molar, so the scaling factor is the molecular weight ratio -- Cl2 has a mol. wt of 70.9; Br2 has a mol. wt of 159.8.)

When would I ever need to use baking soda? (I.e., what is the purpose of a second buffering system when there's already one trying to maintain the pH levels?)
If your pH is acceptably stable, than you don't have to increase your carbonate alkalinity. However, with concrete pools, it's necessary to approach calcium carbonate saturation levels, to avoid reaching saturation by dissolving the pool walls.