FC depletion rates

Rick T

Well-known member
Apr 28, 2019
109
Houston, TX
Does FC deplete daily at the same rate regardless of its level? I have a CYA of about 80 (used to be 100 so I drained 14" out to get it to 80). I have been keeping the FC level around a 10. I lose about 4ppm/day here in Houston and this requires me to add about 1/2 gal of 10% liquid bleach/ day in the summer. If my CYA was 50 and I could then lower my FC to the chart level of 7 would I still need to add 1/2 gal daily? Does the FC burn off at the same rate regardless of the CYA and FC level? I've done the overnight test and I am well within the acceptable limits and my water looks clearer than ever. Thanks.
 

duraleigh

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Apr 1, 2007
34,437
Sebring, Florida
Does FC deplete daily at the same rate regardless of its level?
It's a percentage loss. There are some variables but let's say your FC is 10 with a CYA of 80 and you lose 4 ppm (which you currently do). You lose 40% of your FC daily.

Now, if your CYA is 60 and you keep your FC down around 5, 40% of five now becomes a 2 ppm daily loss.

It's a little more complex than that but the principle is solid.

This late in the swim season, it may not work cost wise to drain 8k of pool water to reduce your CYA to 60, but the FC savings should be real.

PS - losing 4 ppm in your pool and geographic climate is a little excessive. Have you performed an OCLT? You may have some algae (invisible so far) consuming some of that chlorine.
 

Rick T

Well-known member
Apr 28, 2019
109
Houston, TX
I did an OCLT a few weeks ago and it passed. Water is clear as ever and no visible algae. Just wondered how high CYA (80) would affect the burn-off rate of FC. Either by protecting it (with residual stabilizer) or by hurting it because of the higher level needed to maintain chart levels.