Pool calculator and granular chlorine

lancer1991

Member
Feb 17, 2008
19
First time pool owner and still trying to learn the ropes. I have a 12,200 gal colored plaster pool with a SWCG and a Starite System 3 Mod Media filter. My question is, when I get low chlorine readings and plug it into the Pool Calculator, I get no amount by volume. As I picked up some granular trichlor chlorine I'd like to now how much I should be adding when needed by using a measuring cup.

Thanks.
 
G

Guest

I would not recommend using trichlor or dichlor with a cartridge filter (which the Mod3 is, whether it has the DE option or not). Your SWG should havbe been set up with the proper CYA level and using stabilized chlorine will cause this to rise.

Also, granular trichlor is ususally sold as a black algae treatment because it is slow dissolving and will sit on the pool floor. Great if you are trying to kill black algae and need to deliver continuous chlorine to the algae spots but not so good if you are just trying to get more chlorine in your pool.

If you are getting a low FC reading with your SWG you either need to increase the pump run time, output percentage, or check your CYA level and make sure it is in the recommened range! (Possibly all three!)
 

lancer1991

Member
Feb 17, 2008
19
Since I have already purchased a 20lb container (couldn't find anything smaller except the 5lbs of 1lb bags), what would you recommend. I'd rather not waste the $60 or so it cost.

My tests tonight had the following:

T/A=100
FC=7.5
CC=0
TC=7.5
PH=7.8
CYA=>20 (dot never went away and this would match what I was getting with test strips)
 

muss08

In The Industry
Mar 22, 2008
56
Maryland
Your FC level seems fine- even high if your CYA is really 20. I would recommend getting your CYA up to 50 or 60, and getting your TA and pH down to 80 and 7.4
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
I think you meant CYA <20>= and yes, you can use your Trichlor pucks as your source of chlorine in order to get your CYA higher, but it will take a while. For every 10 ppm FC added by Trichlor, it will add 6 ppm to CYA. Also, Trichlor is very acidic so you'll be needing to add something to raise the pH such as 20 Mule Team Borax and over time probably Baking Soda as well.

You probably got low FC readings using your SWG because the CYA was too low so chlorine was getting broken down by sunlight too quickly. Normally, you wouldn't get Trichlor, but if you can't take it back, then the above is a slow approach to getting the CYA up to the 60-80 ppm range that should work well with your SWG. Next time, get chlorinating liquid or unscented bleach (e.g. Clorox Regular or off-brand Ultra) if you need to add extra chlorine.

Richard
 
G

Guest

Are you sure what you have purchased is trichlor?
Also, if you could post a full setof test results it would be helpful.
 

lancer1991

Member
Feb 17, 2008
19
waterbear said:
Are you sure what you have purchased is trichlor?
Also, if you could post a full setof test results it would be helpful.
I purchased Aqua Chem Chlorinating Granules Plus that says it has 71.8% Trichloro. Test results are above, I think only thing missing is a salt test.

muss08 said:
Your FC level seems fine- even high if your CYA is really 20. I would recommend getting your CYA up to 50 or 60, and getting your TA and pH down to 80 and 7.4
I'm trying to bring my PH down. Put in 29 ozs of 31.45% muriatic acid last night and 32 ozs night before and still running high. Just filled this new plaster pool about 2 weeks ago now.

chem geek said:
I think you meant CYA <20>=
I was trying to say that it was less than 20 as I filled it all the way to the top and was still seeing the dot, so I assumed it was less than that.
 

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
32,859
Sebring, Florida
Lancer,

Thru no one's fault, this thread has gotten a little confusing.

Generally, you are in good shape.

1. New plaster pool is almost always gonna' have continual pH rise. Keep pouring in the muriatic to counteract that and DONT let it get above 8.0 (which it will do if you don't keep adding acid.)

2. FC could come down a bit to around 3-5ppm....If that's a result of the tri-chlor no big deal. If it's a result solely of your SWG, turn it down a little.

3. You definitely need to get your CYA up to around 60ppm....add some more

4. Alk will come down with pH...leave it alone for now.