All good but low FC


Well-known member
May 11, 2010
Dallas TX
Excuse the long post - I've tried to add all the relevant info :blah:

My new (to me) pool seems to like low FC for some reason. I bought the place Oct '09, so this is the first season I've been managing the pool.

33k gallons gunite
Clearwater SWG
DIY acid dosing system
DE filter
Salt 3200ppm
pH 7.5
FC 1
Temp 90F
CC 0
Borates 50ppm
Ch 420
TA 80
CYA 100
no overnight CL loss

Only thing that jumps out is low FC. It's been cruising at 1ppm since the pool opened in March. Water has been around 90F for a month. I'd expect to see issues by now if it was going to happen.

No algea, no scum, no smell, nothing. Water is gorgeous.

Once I shocked it up to 40ppm :whip: . It slowly stabilized right back to 1ppm.

Once I kept it at 10ppm for a week using bleach, according to the CYA/FC chart. The pool smelled like CL and stung our eyes. So I let it go back down.

Pump & cell run 6hrs a day, right at about 1 turnover. Cell setting is 100% output. Cell is the 24k model, a bit undersized. Cell seems to make lots of CL in the bucket test.

Once the pump lost prime and did not pump for 2 days (poor gasket seal). Water turned slightly cloudy, cleared back up in 6hrs of running. This tells me the pool is pretty dang stable :sleep: , nothing going on.

Numbers are from the 'big' test kit. The FC readings from the various tests, strips, and pool store are consistant.

Such low FC numbers have been bothering me all season, but I'm tempted to shrug and accept it :cheers: .

Any thoughts?

Bama Rambler

Mod Squad
TFP Expert
Bronze Supporter
LifeTime Supporter
Jun 22, 2009
SouthWest Alabama
You already hit on the answer. "Cell is the 24k model, a bit undersized" There's your problem right there. It's almost 30% too small. And only running 6 hours a day. No wonder you're not making enough chlorine.

Melt In The Sun

TFP Expert
LifeTime Supporter
Oct 29, 2009
Tucson, AZ
To build on what Bama said, more pump run time will help get your FC up. It needs to be higher; you've been lucky so far, but I wouldn't push it.

If you got a strong chlorine smell and stinging eyes at 10 ppm FC and 100 ppm CYA, something else was wrong. That level will not sting eyes.


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
Any thoughts?
It appears to me you have managed your pool quite well despite being outside normal parameters. I think you're cutting it too close on FC.

If it were my pool, I would never allow the FC to dip below 3-4ppm. With the slightest slipup in your management, you can get an algae bloom that will take you a ton, A TON, of chlorine to clear up because of your CYA being so high.


Well-known member
May 11, 2010
Dallas TX
hmmm thanks for the input.
I'm kinda unwilling to increase the pump runtime to generate more FC, spinning that big motor is spendy. 6hrs seems to be the sweet spot for keeping the water looking good, and running the vacuum enough to clear small debris.

Would suppliment with Bleach to 4ppm be OK? I could probably rig an auto-doser in addition to the acid doser. Once the cell dies, a bigger one can drop right in, correct?

Melt In The Sun: the CL smell & sting was noticeable but not terrible. I guess we're spoiled.