Interpreting FC increase & SWG percent

[loripanori]

Hi there, we have a new pool with an ichlor30 just filled a few days ago. Salt was added to 3600 and CYA to 40 as recommended by the instructions.

I am a bit confused about the pool math calculator. If we run the pump for 16 hrs at 40% it says this will increase the FC by 2.0 ppm. I know some of this will burn off. So if I want to maintain the FC at 2-3 ppm do I need to run at a higher percentage? I don’t want to run it so high that the FC creeps up every day.

I guess I’m having a hard time figuring out how to set the SWG for a stable chlorine level. Is it just trial and error?

 

[loripanori]

Also, the manual recommends 40 CYA. However, everything I see on this site suggests CYA should be higher in a salt water pool (70-80). Should I go by the recommendation in the manual? Or increase it?

Thanks!

 

[PoolStored]

So if I want to maintain the FC at 2-3 ppm

I would recommend that your run your FC at 6-7 for a CYA of 40. 2-3 is flirting with algae, and give you zero room for a large FC demand day. Always follow this...Link-->FC/CYA Levels

Is it just trial and error?

Basically. After a year, you will get a feel for the right amounts for each season. If you have a variable speed pump, you might consider running it on low speed, 24/7.

I don’t want to run it so high that the FC creeps up every day.

It might creep up, then turn it down a bit. It is perfectly fine if your FC (for CYA of 40) runs up to 9-10 or down to 5-6, just make adjustment to keep it close to 6-7.

It is also perfectly safe for people and pool up to FC 16 (SLAM level) with CYA of 40. In general, divide your CYA by 10 and multiply by 4, and that gives you the max safe FC. (40/10)*4=16.

 

[PoolStored]

Hi, I have a newly filled salt water pool with an ichlor30 SWG and the manual recommends 40 CYA. However, everything I see on this site suggests CYA should be higher in a salt water pool (70-80). Should I go by the recommendation in the manual? Or increase it?

We are coming into the fall and FC demand is going down. I think 40-50 is just fine for the remainder of the season.

Next year, use 60 CYA until you are confident in your ability to maintain your FC at the top of the target range. When you are confident, then raise it to 70-80.

 

[mknauss]

Should I go by the recommendation in the manual? Or increase it?

If your location is Ontario Canada, then 40 ppm CYA right now is likely fine. A bit low but you are heading into winter in a week or two so no real reason to raise it.
Next spring, in late May early June, I would suggest you raise the CYA to 70 ppm for the summer. Your SWCG will last much longer.

 

[loripanori]

thank you for your replies! I guess I’m confused, because a lot of places say that free chlorine should be 1-3, or 2-4 ppm. I know some of this binds to CYA which prevents it from working. But if I go up to 6 or 8 ppm of FC won’t it feel/smell very chlorinated?

 

[proavia]

thank you for your replies! I guess I’m confused, because a lot of places say that free chlorine should be 1-3, or 2-4 ppm. I know some of this binds to CYA which prevents it from working. But if I go up to 6 or 8 ppm of FC won’t it feel/smell very chlorinated?

Those places don't take into account that some of the chlorine is bound to the CYA.

Even at SLAM leve of FC 16 for CYA 40, you really won't smell "chlorine".
The smell you may be familiar with actually isn't the chlorine, it's the biproduct of the chlorine killing nasty stuff or it can also be ladk of sufficient chlorine for your CYA level.

 

[TinFoilHat]

"those places" don't care that we follow the chemistry and not the symptoms. Just follow what is recommended and advised here and you'll have a clean and sanitized pool to swim in all of the time. Stay out of stores and away from pool services.