I have a couple of pools that operate solely on chlorine pucks. My problem is that so many pucks are needed to keep the FC levels maintained in these pools that the CYA level jumps much too quickly. During a typical week we might use as many as 15 pucks (3 kilograms of pucks) to keep the FC level in the 2-4 range. In less than two months, my CYA levels are now at 60 - with two months to go. These are pools that fall under the definition of commercial by the public health act here, and have to be maintained according to that regulation...as such, I am limited to a legal CYA range of 30 to 80.
I currently use BioGuard Basic Tabs (formerly known as Tabguard Tabs), which are a standard 200g 100% trichlor puck. To my knowledge there are no "safe to use" puck products that lack cyanuric acid, or at least have less of it ... ? Near as I can tell, the people before me used ProEI and other typical 200g pucks, simply loading up the feeder with no regard for FC (their test kits only went to 5 and the log says 5 every day!) or CYA (rarely or never tested according to their logs).
These are massive pools (somewhere in the 180,000L to 350,000L range, I'm trying to figure that out right now), one of which takes about 10 days to fill with the available water supply, so I don't want to dump and refill if I don't have to. Last year I "held out" by adding 20% liquid chlorine on a daily basis from July to September, as it was the cheapest option, adding pucks only for the weekends when volunteers are watching the pool. This year I've started adding 60% or 70% calcium hypochlorite, since the pools needed a little more calcium anyway, and will be ordering liquid chlorine soon if I can't figure something else out.
What else can I do besides manual chlorine addition (not technically legal) or dumping water?