How much will 4 pucks raise CYA?

[chem geek]

One Tri-Chlor 3" diameter puck (which I weigh at 8 ounces or half a pound) will add 4.06 ppm of chlorine and 3.33 ppm of CYA in a 10,000 gallon pool so you can calculate accordingly remembering that a larger pool would have smaller amounts (i.e. multiply my numbers by 10,000 and divide by your pool size in U.S. gallons).

I think the bigger concern is that it will take a while for your pucks to dissolve. In a floater, it usually took 5 days for my pucks to dissolve and even stupidly putting it in the skimmer (which should NOT be done to due its high acidity) it still took a couple of days to dissolve.

If you are desparate, I suggest you crush the Tri-Chlor tablets (with a large mortar and pestle if you have one), put it in a sock or something similar (pantyhose?) and hang it near a return outlet with the pump running. Hopefully, if you are lucky, the pucks will dissolve in a day or less. Please use gloves and remember that the stuff is acidic (so some gloves may not handle that well).

Note also that in a 10,000 gallon pool with TA of 100 and initial pH of 7.5, the pH will drop by 0.12 for one puck PLUS the using up of chlorine will drop the pH another 0.16 so a total of 0.28 so you'll have to add about 13.5 ounces (weight) of Soda Ash (Washing Soda; Calcium Carbonate) or about 5.4 ounces (weight) of Caustic Soda (lye; Sodium Hydroxide) or about 25 ounces (weight) of Borax. The amount of base you have to add is per puck regardless of the size of your pool.

Another alternative is to get something to cover your pool to prevent the sunlight from hitting all or most of it. Without CYA, direct sunlight will cut your chlorine level in half about every 35 minutes during peak noontime sun! Even 4 Tri-Chlor tablets in a 10,000 gallon pool raising CYA to around 13 will only improve this half-life up to 1.5-3 hours, but that's better than nothing.

Kind of makes a 30 minute drive not sound so bad, eh?

By the way, do you have any idea how your CYA got down to 0? Do you frequently backwash your filter (is it DE or sand) and/or have lots of splash-out or any drain and refill of water?

Richard