Hi guys, I am a pool professional(serviceman) from the Boston area, and completely new to these threads. I have seen many strange things over my years in the industry, and finally want some answers! So I have read through some of these and other threads, and it seems to be pretty much agreed that the only way to lower CYA is by drain/refill. There seems to be an old rumor about ammonia, but that has been debunked. Well, I have serviced a high end gunite pool on the ocean for about 4 years now, and something strange recently happened. On Thursday, the pool was looking great and everything tested within normal ranges. By Monday (I service it twice a week), it was a complete swamp. It is salt water pool, with CYA around 70 and FC around 4 on Thursday. On Monday, FC was 0, and so was CYA! After a little investigation, I found fertilizer pellets around the pool area - they had their lawn treated, and it rained over the weekend. It did introduce low levels of phosphates, as expected. I brought the pellets to a landscape/nursery place that I share a parking lot with. They told me it was a product called Weed and Feed, made by Scotts I think. I wasn't surprised this dropped out the FC and added phosphates, but to completely neutralize the CYA? As far as I can tell, there is a chemical in that product that can lower CYA. So this leads me to believe that CYA CAN be lowered other than drain/refill, which would help when I come across too high levels and people don't want to spend money on water. Any insight would be appreciated! Also, stay tuned for some of my upcoming posts about other strange situations I have encountered.