Trichlor & PH

[Simmons99]

I know that trichlor lowers PH and contains CYA. When I started up the pool last week - I filled a floater with 9 1" Trichlor tabs. Since the pool is plaster - it will help keep my PH down and add CYA.

Test results yesterday morning (dialed back the floater 1/2 way):

FC=5 (OTO)
TC=5
PH=7.5
Alk=90

and this morning I get these numbers:

FC=1.5 (FAS-DPD)
TC=1.7
PH=7.2
Alk=70

Is the PH drop more than likely linked to the trichlor in the floater - even though I reduced the flow on it?

Also at what point should I start testing for CYA? My chlorine level has remained (before I cut back the floater) between 3ppm-5ppm in the morning and 0-1ppm after a day in the sun. Should I wait another week?

[PatL34]

I would start testing straight away. I was using trichlor to add cya, and it will be there before you realize.

Pat

[aylad]

Yes, the pH drop is likely due to the trichlor. I would wait about a week or so after you started using the trichlor to test for CYA. If you didn't add any additional CYA besides what's in the pucks, it will take a week or so to rise to the point where your test will pick it up.

Janet

[duraleigh]

Your FC drop of 3.5 over 24 hours (with tri-chlor present) might indicate you've got some organics in the pool and may need to shock. Have you had the pool long enough to establish a daily chlorine loss?

[Simmons99]

The pool builder wouldn't let me add any chlorine until Sunday 8/20- so no I haven't. Of course the first couple of days the sun burned right through it - so it was zero in the evening - I'd add enough bleach to get to about 5ppm, but held through the night.

I have not added any CYA - except what is in the pucks. I added about 2 1/2 gallons of bleach between Sunday and Monday, but haven't had to add any since then - on Monday evening (between the bleach and the pucks) I had .5ppm-1ppm at sunset. Tuesday evening - I had 1ppm without any additional bleach. I didn't test last night (had class)

Also - I expect that there are "some" organics in the water - we've had the dog in and the kids every evening. Plus there is some dirt/sand in the bottom of the pool, PB says the finish manufacturer won't warranty damage from the little robot vacuums if you use one in the first 28 days - so that could cause some depletion.

I hear that it takes a lot of reagent to complete this test and I don't want to test unnecessarily.

[duraleigh]

I misunderstood your stage of development.........of course that explains your FC drop....Sorry.

On another subject, are you trying to establish a decent CYA level with just pucks? That probably won't work too well....it'll take a long, long time.

[Simmons99]

I have "pool school" on Friday and the builder has been coming out during the day - he doesn't like to talk to me about chemicals and just does what he wants so I am afraid that they will want to add some later - so I figured I would wait until they stop coming over and then I would test and add - I would hate to add some and find out they did too!

.... then I thought if they don't add any CYA - I would be able to figure out how much CYA is being added to the pool per puck - there seems to be a lot of people asking that on the forum, and since I just filled I know there is none in there.

But since I have no clue as to how much is being added - I asked to make sure I don't accidently overdose the pool. It doesn't sound like that is likely.

Sorry for the rambling ---- too much coffee today.

[giroup01]

I would be able to figure out how much CYA is being added to the pool per puck - there seems to be a lot of people asking that on the forum
I'm from Canada so I'll go metric on you.

Say each puck weighs 200 grams and is 100% trichlor. Trichlor is 55% stabilizer by weight therefore 200 grams * 0.55 = 110 grams, so each puck, by weight, is 110 grams CYA.

110 grams in 10000 liters water is 0.011 grams/liter, or 11 mg/L, or 11 ppm, therefore each 200 gram trichlor puck you add to 10000 liters of water increases the CYA by 11 ppm.

For 14000 gallons, that's 52996 liters therefore 2 ppm per 200 gram puck.

[Simmons99]

cool - no one has been able to answer that before - thanks!