FC/CYA balance


Active member
Apr 9, 2020
Gold Canyon AZ
We're snowbirds with a "pool boy" ;) watching over our pool once a week all summer while we're gone. I've decided to take over pool duties (5850 gal cocktail pool) for the winter partly due to the chlorine and cyanuric acid levels he's left me with. I have my own strip testers and a basic Taylor kit (that doesn't test for CYA) but I took a water sample to my local Leslie's for a starting point. My FC was 0.04 and the CYA was 124. I've learned the only way to lower CYA is to dilute the water so I dumped 1/4 of the pools volume and added a gallon of liquid chlorine. Now my CYA is 106 (getting there!) with FC at 0.96. I'm going to need to go thru that procedure at least 2 more times to get the CYA to a reasonable level. I'll be using strictly liquid chlorine for the remainder of the season. I understand why the pool guy who only sees the pool once a week during the summer would use trichlor tabs for convenience, but with the tabs adding more and more CYA each week, how do I avoid the crazy build up of CYA requiring yet another water dump? Seems to me that using a product that continually adds an ingredient to the water that is hard to get rid of is counterproductive. How do you all keep the CYA at reasonable levels? Seems everybody is using the pucks; they're everywhere! Just doesn't make sense.


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
I suspect your CH level is also quite high unless you use soft water for fill water. It would be best to drain the entire pool and start over.


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
If it doesn't make sense, Please read "The "ABC's of Pool Water Chemistry" up in Pool School......then ask questions and we will all help it make sense.


Gold Supporter
May 20, 2020
Katy TX
Pool Size
Liquid Chlorine
Not sure what's going on here
I think the concern is that pool store testing is unreliable and inconsistent. Also, when you do your own testing you have a much better understanding of the dynamics such as FC levels vs. CYA levels. If your original CYA was truly 124 (we round up to 130), the target CYA should be 40-50. Therefore you would need to drain and replace 60% of your pool water. So now after draining and replacing about 25% of your pool water you are at 110 you still need to drain and replace at least 50% of the current pool water. That is if you can believe the CYA values provided by the pool store. Similarly with Calcium, if it is too high then you can only reduce it via draining and replacing water. However, you may be adding Calcium when you fill the pool back up. Tap water can contain Calcium but not CYA. It would be good to test your fill water to determine how much Calcium you may be adding as well.
If you can get a proper test kit Test Kits Compared and read up on Recommended Levels that will provide you a good base.

The alternative to pucks is to use Liquid Chlorine (LC) as you indicated but as stated by Marty, the addition of a Saltwater Chlorine Generator (SWCG) would reduce your manual dosing of LC and possibly reduce the need for your "pool boy" unless he is doing other things to maintain your home than adding pucks to the pool while you are not there.


Active member
Apr 9, 2020
Gold Canyon AZ
Yeah, CH is at 300. I'm going to try draining 1/4 of the pool twice more over the next 2 weeks and check the CYA as well as the CH after that. I understand that the pool store can't be trusted 100% but I thought it might be good for comparison week to week. My test strips confirmed high CYA although the exact number can not be determined. I have a better Taylor test kit ordered. A SWCG would be great if I could afford it. Truthfully I'm more likely to spend that kind of money on an auxiliary heater to augment my solar. I've been studying the info on FTP for quite some time. I think I have a pretty good handle on what levels I'm aiming for. I'm looking forward to trying out my new test kit. Thank you all for your helpful responses.