Well... besides just adding chlorine, you're also adding stabilizer, which means the FC level needs to be raised a little more to cover that, which adds more stabilizer, which means the FC level needs to be raised a little more to cover that, which adds more stabilizer, which means the FC level needs to be raised a little more to cover that, which adds more stabilizer, and so on until suddenly you have "chlorine lock" and "high TDS" and the pool store guy, having emptied your wallet, tells you you need to drain.
Oh... and you're also lowering pH pretty substantially with every puck you feed the pool. Check out
Effects of Adding Chemicals in
http://www.poolcalculator.com/ Every pound (2 pucks) will lower pH in your 33000 gallon pool by .19. Which is fine if you have really hard water, but if not, don't forget to add the cost of the soda ash and baking soda you need.
Here's a little comparison I wrote a few weeks ago
We'll take a 16000 gallon pool, because that's what I have. On a fresh fill, prominent national pool chain recommends 2.5 pounds pf stabilizer per 10,000 gallons, which works out nicely to 4 pounds which brings CYA to 30.
With an average loss of 2 PPM/Day or 14 ppm/week, I'll have added 8.6 PPM/CYA if I used trichlor pucks perfectly. And they recommend a weekly "shock" of dichlor between 5 and 10 FC.... 2-3 oz per 10,000 gallons. Split the difference; I'll add 4 oz. CYA went up another .9.
So..by the end of week one, I have added 9.5 more CYA. It is now 39.5. Mimimum FC for that is 3, so I'm probably okay.
Week two, up to 49 CYA.
Week three, 58.5. Minimum FC should be 5, but they recommend 3 as ideal, so the pool looks a bit hazy. So I'll toss in a little extra dichlor "shock" to jack FC up to 10. Which adds another 6.4 CYA. Keeping count? We're up to 64.9 now.
That caught the algae just in time.. we had two weeks of good luck. A steady diet of pucks and 4 oz. "shock" each week only added another 19, up to 73.9 now.
Week 6 it started looking funky, so we "shocked"it once again. CYA is up to 99.3. But minimum FC to keep algae at bay is 8, and we're still holding things to 3, because prominent national chain's preprinted sheet shows that as ideal. So algae got a toehold and the pool has a bit of a tint. So we throw two whole bags of dichlor in which jacks it another 7.6 by the time week 7 is over, we're at 116.4, because we had pucks in the floater the whole time.
So...in 7 weeks, from 30 to 116.4. Let's say there are no more algae outbreaks because they sold me a huge bucket of phos-free and another of yellow-out monopersulfate "shock" Nothing but the pucks and the extra 4 oz of dichlor "shock" weekly. So the next 7 weeks added 66.5, which brings the total to 182.9 CYA.
Now if we didn't understand this and things looked a bit hazy, we might throw an extra puck or two in the floater every couple weeks, which will drive it over 200 easily.
And then next year when you try to open, you're whining here how you "shocked" it and it's still green. And then you get indignant at the cost and bother to drain 3/4 of the pool. Seen it over and over and over and over here.
You're certainly free to maintain your pool with whatever products you prefer - dichlor, trichlor, and Cal-hypo can all have their uses. The source of the FC isn't important; what IS important is understanding what is happening and not overusing the wrong chemical.
