PH and pucks

[aguaguy]

Just read a thread that states that pucks get your Ph all out of whack. Is this so, and if so can someone explain the relation of the two.
I have a fiberglass pool completed this June and have been trying without success to raise my PH above 7.
I tried Ph up and then switched to Borax. So far I have put in about 2 lbs of Ph up and a box (4-5lbs?) of Borax. Ph is still sitting at 7

[mbar]

The trichlor pucks have cya in them, which is acidic - it will keep bringing down your ph, as well as add cya to your pool. You will have to bring up your ph all the time. One way to stop the cycle is to use a combination of pucks and bleach - or just bleach as many of us do on this forum. Also check what your alkalinity is - it is what stabalizes the ph. Your alkalinity should be between 80 - 120.

[waste]

Aqua, if you have a little time, Richard (or one of the other 'chem geeks') will tell you exactly what's happening - I often need a beer or asprin to help absorb the info. The pH of the pucks is about 2.5 (which is very! low) so for every 8 oz puck you need to add ~4.5 oz of soda ash (pH plus) per puck to keep your pH within the proper range. (thanks Richard!)
In addition to the pucks constantly lowering the pH, they also raise your cya. Cya needs to be compensated for (see Ben's best guess chart; stickied at the top of the "using chlorine..." section of the forum) by adding more chlorine than your 'pool dude' would suggest.
Having added so much pH increaser, I wonder if your test kit is still good.
My best advice is to post a full set of numbers and see what the 'real' experts say, I might even be able to help, if I know your chem numbers;)

[chem geek]

In a 10,000 gallon pool, one 8-ounce Tri-Chlor tablet (the 3" kind -- some are 6 or 7 ounces, but I'm using 8 ounces in this example) will lower your pH by 0.1, will add 5.48 ppm Free Chlorine (FC), and will add 3.3 ppm Cyanuric Acid (CYA) as well as increase your Total Dissolved Solids (TDS) by 7.4 ppm. Obviously, a larger pool scales these numbers down accordingly (proportionately). I assumed a TA of 100 with a CYA of 30 and a starting pH of 7.5 for the purposes of calculating the pH drop. To get back to the 7.5 pH, you would have to add either 4.7 ounces of Soda Ash (Sodium Carbonate) or 9.2 ounces of Borax.

The bottom line is that Tri-Chlor tablets are very acidic so you will always be fighting low pH if you use them. And just as bad, as was pointed out, you keep adding CYA to your pool. If you don't have much CYA then this can be OK for a while, but generally once you get to the CYA you want, you don't want to add any more. If you used liquid chlorine (or bleach) instead of Tri-Chlor, then the increase in pH from the initial liquid chlorine addition is exactly compensated by the acidic process of the chlorine getting used up so that you net out with no pH change (technically, there is a small rise from additional base in the liquid chlorine, but this is pretty small).

Richard

P.S.
The pH actually drops even further when the chlorine gets used up since that is also an acidic process. So when the 5.48 ppm of chlorine disinfects and kills bugs or oxidizes organics or gets broken down by sunlight, the pH from this process and the original Tri-Chlor results in a pH drop of 0.24 and requires 13.3 ounces of Soda Ash or 26.3 ounces of Borax to restore the pH. If you used liquid chlorine (or bleach) instead of Tri-Chlor tablets, then the increase in pH from adding liquid chlorine pretty much exactly compensates for the acidity from the chlorine getting used up so that you net out with virtually no change in pH. This means you will use less acid or base when using liquid chlorine as your primary source of chlorine.

[aguaguy]

Thank you all especially Chemgeek ( I knew my chemistry classes would pay off someday) It looks like no more pucks for me. They were fed through a "Frog" auto chlorinator which the PB raved about but never could even keep a constant level of chlorine (what a waste).

FC 3.5
CC 0
PH 7
TA 100
CYA 35
6600 fiberglass pool