I've had an issue with my FC being consistently low for about 3 years. I joined here to take control and since i did, It's been better, but not perfect. I just found a fix for my specific problem and figured that i'd post it, in case it's of any help to someone else.
Circumstances (dead bird in skimmer and me 120 miles away) forced me to have my wife purchase a powdered shock that i probably would not have bought had I been home and had a choice. This specific shock contained a trace amount of copper as an algecide. I had my wife put 1 lb of this in the pool until i got back to civilization. Bottom line...my pool has been sparkling clear for about 7 weeks and the FC is now measuring in the 3-5 range consistently. The copper algacide is the only thing that I've done differently, so I have to assume that this was the fix for me. (unless you want to try putting a dead bird in your skimmer )While this may not be the fix for others, that was the best $5 I've spent on my pool in about 3 years. Now I am able to maintain using BBB and keep FC at a respectable level.
BTW, I couldn't do any of this without the TFT Test Kit.