This is something that I've known for a long time. There is a post about it from some time ago:
Degradation of Cyanuric Acid (CYA))
Higher temps in hot tubs speeds this up. Higher chlorine levels do as well.
Some folks report that their cya levels don't drop very much over time. I have no reason not to believe them, but it's not my experience with my hot tub. I still need to test for cya levels frequently because I cannot predict what the test will say before running it. I frequently shock my tub up to the shock level on the cya/fc chart. Cya needs to be added back at roughly 1ppm per day averaged out over time in my hot tub.
The other week I was out of town and I asked my wife to add bleach to the tub, but we had ran out of bleach. She bought a half gallon of clorox from the gas station up the road to use. When I got home, I just assumed that the gas station bleach was old and stale, and just dumped the rest of it in and then threw the bottle away. I even added some more regular bleach that I had just bought on top of the clorox at the same time. As it turned out the clorox wasn't so bad. When I ran the tests about an hour later, my FC was running 80ppm. My CYA was at about 80-100, when I had tested it a week earlier.
This shocking event drove my cya levels down to about 20-30 when I tested it again the next day.
It also broke lose a bunch of bio-film from the plumbing. I did the best I could wiping out that dark bubblegum from the waterline with paper towel, then added some ahh-some to see if I could bust lose some more. The bleach seem to have gotten the vast majority of it, so I just skimmed off the foam and didn't change out the water.
The water has been extra clear this week like what happens when I buy a new filter. I also ordered a new filter to put in, but haven't done so yet.
How often does TFP recommend new filter replacement?
This new one will be our 5th filter since we got the tub 2.5 years ago. So, I guess that averages out to a new filter every 6 months. Does that sound about right?
Edit to note: my tub has only one filter. I see in pictures that others have multiple filters on their tubs. So, I suppose that makes a difference.
Degradation of Cyanuric Acid (CYA))
Wojtowicz also shows a strong temperature dependence on the chlorine oxidation of cynauric acid where every 10F increase in temperature results in roughly doubling the rate of degradation. So his data was with pools at 85F so pools at 90F could have degradation rates about 1.4 times higher.
Higher temps in hot tubs speeds this up. Higher chlorine levels do as well.
Some folks report that their cya levels don't drop very much over time. I have no reason not to believe them, but it's not my experience with my hot tub. I still need to test for cya levels frequently because I cannot predict what the test will say before running it. I frequently shock my tub up to the shock level on the cya/fc chart. Cya needs to be added back at roughly 1ppm per day averaged out over time in my hot tub.
The other week I was out of town and I asked my wife to add bleach to the tub, but we had ran out of bleach. She bought a half gallon of clorox from the gas station up the road to use. When I got home, I just assumed that the gas station bleach was old and stale, and just dumped the rest of it in and then threw the bottle away. I even added some more regular bleach that I had just bought on top of the clorox at the same time. As it turned out the clorox wasn't so bad. When I ran the tests about an hour later, my FC was running 80ppm. My CYA was at about 80-100, when I had tested it a week earlier.
This shocking event drove my cya levels down to about 20-30 when I tested it again the next day.
It also broke lose a bunch of bio-film from the plumbing. I did the best I could wiping out that dark bubblegum from the waterline with paper towel, then added some ahh-some to see if I could bust lose some more. The bleach seem to have gotten the vast majority of it, so I just skimmed off the foam and didn't change out the water.
The water has been extra clear this week like what happens when I buy a new filter. I also ordered a new filter to put in, but haven't done so yet.
How often does TFP recommend new filter replacement?
This new one will be our 5th filter since we got the tub 2.5 years ago. So, I guess that averages out to a new filter every 6 months. Does that sound about right?
Edit to note: my tub has only one filter. I see in pictures that others have multiple filters on their tubs. So, I suppose that makes a difference.