Roguewave, here. 10 year lurker, first time poster. There is no doubt in my mind that this is the best place on the web for pool care advice and I appreciate all I've learned from many of you over the years.
Forgive the long post, but consider some of it my introduction.
20,000 gallon, 16x32 vinyl lined, in-ground, diving pool.
9 Fafco panels and a Compool controller. Our pool season generally runs April 1st through the end of October and we're in it almost every day we're home.
Currently using trichlor pucks until CYA rises to where I want it for a given season and then bleach.
This morning's parameters:
CYA - 60
Cl - 5.5
pH - 7.5
Al - 90 (added 38 oz of baking soda this morning)
CA - 80 (here at TFP I learned not to concern myself much with CA for this vinyl pool)
CC < 0.5
Haven't had to shock to lower CC yet this year. The cover is normally off all day, which probably helps (according to this site.)
On the advice of the pool installer, I installed an ecomatic SWG when the pool was new about 10 years ago. Well... the cell had a long life, but finally gave up the ghost a couple of years ago. Now since ecomatic has gone the way of the Dodo, I looked into aftermarket cells and the reviews of their quality were pretty awful.
So... without the budget to replace the ecomatic entirely, I was forced to switch to the old standard approach.
I keep my parameters tight. Alkalinity never gets beyond 90 or 110. pH almost never off by more than 0.1, Keep chlorine about 1 ppm above the minimum recommendation as per The Pool Calculator. Haven't had any algae blooms in what seems like forever.
We have a week-long, family trip planned in the next month and, rather than run the pump, I plan to leave the cover on and bump up the chlorine with enough liquid bleach to hold 'er 'til we get back (erring on the side of caution, of course.)
I estimate the minimum to be about 4 bottles of 8% (or 7?) Walmart concentrate. So I would probably do 6. With the cover on and a CYA of 60, I believe it's likely we will be coming home to a pool that will need a few days with the cover off.
According to chem geek's chart, I estimate I need about 10 bottles, total, to shock.
Using the K2006C, I get < 0.5 CC when using a 10 ml sample. The reagent does turn it a hair pink and one drop returns it to clear. But the funny thing is, when I use the 25 ml mark, I can't get the sample to return to pink no matter how much reagent I use.
This is puzzling, but I feel it's OK to figure that I don't have much CC.
So... my question is...
Would it be worth it to go ahead and shock... figuring that I would probably have to add some thiosulfate upon our return?
Or would just a moderately elevated level of chlorine finish oxidizing what little CC I have?