I have a question concerning the CYA level of my pool. I'm a relatively new pool owner but have done extensive research here and at poolcalculator.com. I bought a house about a month ago with a dark green, very swampy 20k gallon inground pool. Based solely on the information I learned here and on the Pool Calculator (and a little common sense), I had the water in my pool crystal clear and, had the temperature been a little warmer, ready for swimming in a little less than 2 weeks. That's how awesome you guys are!
But, I digress. According to the Pool Calculator, the only practical way of reducing CYA levels is to replace water. That leads me to believe that once you reach a certain CYA level, you shouldn't need to add any more CYA under normal circumstances. In other words, the CYA level shouldn't naturally drift like FC or pH does, correct? However, when I recently went to my local pool supply store to buy some CYA, a salesman tried to sell me some trichlor tabs. Armed with the knowledge that trichlor also adds CYA, I told him that I would rather not be constantly adding CYA. He then told me that unless I used trichlor tabs, I would always need to keep adding CYA and that it was one of the most expensive pool chemicals (he was definitely correct on that front). I pretty much dismissed him, bought a 7 lb bag of CYA, and went about adding it to my pool. I realize that CYA is very slow to dissolve, so I put about a pound or two in a sock, tied it off, put it in my skimmer for about a week until it was all dissolved, then repeated the process. Here is my issue: When I first started this process, my CYA level climbed to about 50 ppm after the first couple of times of adding CYA. However, I've added CYA about 5 times since then, and I can't seem to get my CYA level above 50 ppm. My pool is unscreened and gets a full day of direct, Florida sun, so ideally I would like my CYA level at about 75 ppm.
Any idea what I might be doing wrong? Was the guy at the pool store correct in saying that unless I use trichlor or dichlor, I would indeed need to constantly add CYA? Any words of wisdom you can offer would be much appreciated!