Combine SWCG and Tri-Chlor Floatie?

[Jimmy C]

Hi,

I was wondering about combining the two methods, SWCG and a Floaty with Tri-Chlor pucks inside.

I know this might sound crazy, but hear me out.

With a SWCG most have a rising PH problem, sometimes requiring a lot of acid per month to control.
With a SWCG most have a diminishing CYA problem since we adjust CYA early in the season, and thereafter from splashout, filter backwash, and pool leaks, we lose CYA every month.
With Tri-Chlor pucks most have a diminishing PH problem
With Trichlor pucks we have a rising CYA problem

So if we combine the two techniques, I can see several advantages:

Less Acid needed to counter rising PH
Less CYA powder needed to counter diminishing CYA
Less SWCG on time since the SWCG might only have to work 1/2 to 2/3 as hard as before..
Longer SWCG cell life might be possible

So is this a good idea? :-)

Jim

[waterbear]

Depends on some factors you have not considered. Main cause of rising pH in a salt pool is from outgassing of CO2, which is easily controlled by dropping TA.
As far as CYA decreasing, not all pools will have that problem since not all pools have backwashing filters. For example, my salt pool with cartridge filter, needs to have salt, CYA and borates added about once a year since I lose very little and my levels remain very stable. With my TA at 70 ppm and borates at 50 ppm my acid demand is about a cup every two months, not a whole lot at all. Pool is open year round, btw.

If I started using trichlor in my pool I would need to increase the TA on a regular basis to compensate for the TA that is getting 'used up' by the acidic trichlor and my CYA would soon rise way too high so for me this is not a valid solution.
If someone has new plaster that is adding the the pool's acid demand then I can see a limited usefulness of trichlor but from my experience with customer's pools the speed at which CYA is added is usually much faster than the speed at which it is removed from backwashing and splashout. If the pool was leaking water then this approach might be more useful. I have found that customers with sand filters usually need to bump of the CYA and salt a abut 3 times a year, still not a lot.

[Jimmy C]

Thanks Waterbear,

Well I do have a leak that I cannot find, and I seem to be losing about 300 ppm salt per month which also suggests about 10% of my water over the same time. My sprinkler system fills up the pool 2X per week for now. This is more than evaporation since the salt PPM does not go up as the water level drops. It does drop as expected after topping up the water though.

As to rising PH with a SWCG pool, I thought it had to do with this:

NACL + 2H2O -> HOCL + NaOH + 2H2

(result is: hypochlorous acid + sodium hydroxide + hydrogen gas)

http://poolnerd.com/2007/03/29/salt-...ne-generators/

So the SWCG literally pours a strong base, sodium hydroxide into the pool. The pool folks selling a SWG will even argue that their SWG cells do not produce hydrogen gas, and that any gas bubbles in the return jets are the result of a plumbing leak.

Nice H2 bombs:
http://www.youtube.com/user/griffcre.../1/GJLiXCKts-o

So for now I have resorted to Tri-chlor pucks in my floaty to help keep the CYA more stable, and to take some of the burden off my SWCG.

I will get serious concerning the pool once the summer is over..

Jim

[waterbear]

the chemistry is incomplete in the reaction you posted. Chem geek gave an excellent explanation of the full chemistry in this post.
In a nutshell what is not taken into account is that when chlorine is broken down or used up the reaction is acidic so the net effect is pH neutral. Hydrogen gas is produced at the cathode of the SWCG and this causes aeration of the water that causes CO2 to outgas. It is this outgassing of CO2 that is responsible for the pH rise and can be controlled by lowering the TA to lower the amount of carbonation in the water. This post might help explain why.

Your leak is not normal pool operation with a SWCG so while trichlor migh be of some use in your case it would not be for the majority of salt pools.