I think I have had the exact same experience.
I was using a few pucks just to augment the TFP system and everything had been stable for quite a long time. I stopped using the pucks a few weeks ago and my pH quickly went up and my CYA went down. So I was wondering whether the pucks might have been helping to manage these drifts.
I know it can be necessary, but I hate using muriatic acid.
How many pucks do you typically use?
I don’t use many pucks, perhaps only a total of six pounds in the 2 years I have owned the pool. I bought a small package last August because I wanted to experiment with them while I was home to watch the chemistry so that I would have some idea of what they did to my chemistry before I attempted to use them for a winter vacation when my pool would be open but the water temperature too cold for the SWCG to operate. I was down on my CYA levels anyway after a hot summer, but what I discovered was that floating the pucks lowered my alkalinity to a spot where my pH rise was much more manageable. My fill water has an alkalinity of 290 so with evaporation and topping off, it’s hard to get my TA below 100 even with lots of muriatic acid. I will admit that I’ve never spent days purposefully lowering the TA because I’ve known it would rise anyway. (We store rainwater also for topping off the pool to help keep calcium and TA in check but since July, it’s been all hose water because we’ve had no rain, and the tanks go for the garden and landscaping.)
I did use both liquid chlorine and a few pucks over the winter. We had torrential rains last fall that overflowed my pool and required draining excess on more than one occasion. I believe it was the most rain this area of Texas has received since records have been kept. All that fresh water lowered my CH, my TA, my CYA, and my salt. I haven’t checked my records but I think at one point I actually did add baking soda so that my CSI wouldn’t get too low with the cold temperatures, and I didn’t want to use too many pucks and risk crashing the TA.
It’s been a steady diet of SWCG chlorine and MA this summer until last week when I needed a bit of a reprieve because of back-to-school season. I don’t rely on the pucks to provide my chlorine, though they have bumped it up a bit, but they had as of this morning kept my pH at 7.7 for over a week and brought my TA to 90. The TA is probably up a bit, though, because it was the day we’re allowed to top off the pool (water restrictions). So my puck use this summer has been 4 8 oz pucks that are still not completely dissolved in a floater. My CYA was below levels recommended for my SWCG when I put them in, and even these won’t get it quite high enough, but I’ll retest before considering whether I want to put another in the floater.
I’m certainly not trying to argue against TFP, and I sincerely believe that the education here has allowed me to make good decisions for my pool care. There’s another thread over in The Deep End that I read this afternoon that discusses using both liquid chlorine and trichlor and is worth a read.