cant get FCL to rise except when adding shock

Hi, i’m new here… discovered this awesome forum when googling on how to drop too high combined chlorine.   i solved that by bombing it with the non chlorine shock as per the correct formula.   Now i’m back to an old problem.  i just cannot get my FCL to rise without adding shock.  i have 10,000 gallon pool.  Salt generator.   when i run super chlorinate it jacks up the CCL but not the FCL.   right now i’m at FCL 0.18  CCL 0.16  PH 7.7  ALK 108  CYA 81

i was about similar a week ago…i added Dri Chlor and it got to 1.52 FCL and 0.69 CCL.

one week later and i’m back to FCL 0.18.   I just dont understand why my salt generator is not making FCL.  Like i said when i set it to super chlorinate it will just increase the CCL.  I had done that so much in the past i ran into the problem of needed to bomb it with non-chlorine shock to get it down.    Now i just want my FCL to get up!

thank you for your feedback.

Hello smallpool,

Saltwater generators generate chlorine. That’s all they do. They don’t increase combined chlorine. The amount of chlorine generated is dependent on two factors, the % of chlorine set on the generator and the amount of time the generator runs. 
For your pool size and a CYA reading of 81 ppm, the chlorine level should be kept at 9 ppm.

Since you can’t get the generator to super chlorinate the water you could have several issues:

  1. You may not have enough salt in the water.

  2. The salt cell may need to be cleaned.

  3. The salt cell may be old and needs replacing.

  4. You have organics in the water that are eating the chlorine as fast as the SWG makes it.

If #s 1,2 or 3 don’t apply, you will likely need to SLAM your pool to kill the organics and get the water to hold chlorine


My salt cell is brand new this year!  i got a new one thinking that it wasnt working anymore.   my salt reading is 3,300

how much Di Chlor do i need to add to SLAM it to get it to reach the crossover point?    When i’ve done 3 poounds it gets the FCL to over 1 but it just wont hold it for more than a couple of days.


For water with a CYA level of 80 ppm the chlorine level needed to SLAM the pool is 32 ppm. And it needs to be kept at 32 pm until the water holds the chlorine level. In order to reach that level of chlorine in your pool you would need approximately 5lbs of DiChlor. And you would need to check the chlorine level 2 or 3 times a day and add additional DiChlor to replace the lost chlorine.

That said, I would not recommended slamming with DiChlor. Because using DiChlor causes other issues.  Adding DiChlor also adds additional CYA to the water. 5lbs of DiChlor adds approximately 30 ppm of CYA to 10,000 gals of water. That would bring your CYA level to 110 ppm. CYA levels at 110 ppm would raise the chlorine SLAM level to 43 ppm. It would be a viscous circle. Not to mention that CYA levels above 100 ppm are not recommended and the only ways to lower the CYA level is to drain water and replace it or use a very expensive reverse osmosis process.

The most effective and easiest way to SLAM a pool is with liquid chlorine. Pool chlorine is preferable because it comes in strengths of 10% or 12%. Some pool stores carry liquid chlorine. In my area, WalMart has pool chlorine. The big box building supply stores have pool chlorine. Some Ace hardware stores carry pool chlorine. And in my area, some janitorial supply stores also carry pool supplies including pool chlorine.

Liquid bleach can also be used but liquid bleach strengths range from 5% to 8.25% so it would take a lot more. And there are other caveats with liquid bleach. You don’t want to use a bleach that has scents or any other additives. So that leaves most of the Chlorox bleaches out because they all (except Chlorox sanitizing bleach) contain ColorMax additives. The bleach shouldn’t contain anything other than calcium hypochlorite and inert ingredients.

If you want to learn more about properly slamming a pool, there is an article at InyoPools Here

There is a more in-depth article along with a video Here

If you decide to do the SLAM, you will need to turn the SWG off for the duration of the SLAM.
Let us know if you have additional questions or need additional help.


well i’m choosing DiChlor becuase its safe for vinyl pools.   my 4 year old vinyl pool has some pretty major fading in parts i think its because i had been using Cal Hypo.   should i use the liquid bleach or is Cal hypo okay for a vinyl pool (if say i dilute it in water before dumping into the pool?

In my opinion, Cal hypo would be a better choice because it doesn’t add any CYA to the water. It does, however, add additional calcium hardness to the water. That isn’t a problem unless your CH level is already high.

4 lbs of 65% Cal-hypo or 60 ounces of 73% Cal-hypo would bring the chlorine level to 31-32 ppm. If you don’t dissolve the Cal-hypo granules (or DiChlor for that matter) completely before adding them to the water you run the risk of the un-dissolved granules settling to the bottom of the pool and bleaching the liner.

All of that being said, there isn’t any chlorine safer for vinyl, concrete, plaster or fiberglass pools than liquid chlorine.