Re: Newbie about to start
OK so I redid the CYA test.
jblizzle said:
If you still have the CYA mixture, you can try dumping out half and replacing with tap water and then doubling the result to get a better idea. Or redo the test, but start with 50/50 pool and tap water before adding the reagent and then double the result.
As it happened, I forgot to empty my CYA mixture from when I did the test two days ago. I reread the quote above and then got to thinking about it. If you take an already-mixed CYA mixture (50/50 pool water and reagent) and then dump half and replace with tap, the new mixture is going to be 1/4 pool water, 1/2 tap water, and 1/4 reagent. If redo the test with second method, you have 1/4 pool water, 1/4 tap water, and 1/2 reagent. This latter method preserves water to reagent ratio so that's what I did. (I also looked it up under the "detailed test instructions" link posted above and this is consistent with what is posted there).
Now that I think about it, I could have dumped half of the old CYA mixture, and added tap water and reagent in equal amounts and redone the test. This would have preserved the water to reagent ratio (I'm assuming that is important) and saved me some reagent. But there isn't a graduation on the test bottle between 7 and 14 so to do it accurately I'd have to eyeball it or draw one on the bottle using a ruler. Anyway, I didn't think of this in time and besides I don't know about the accuracy of using CYA mixture that is two days old, so I dumped it and cleaned the test bottle well. I decided to save today's test mixture to test again over the weekend and see if I get the same result.
Anyway, I repeated the test multiple times and got 65 to 70 each time so average x2 gives me a CYA of 135. (This is actually consistent with my guestimation from my first test result above). According to the pool calculator, this means I need to replace 41-48% of the pool water to get to CYA 70-80 for SWG, and 63-78% to get to CYA 30-50 for BBB. I reran these numbers for +/- 500 gallons on volume of my pool, and +/- 5 on CYA and they never changed.
As far as draining, no one drinks from these canals, or eats the fish (which are primarily exotic, but fun for the kids to catch). There are no runoff drains on my street or others in the area. (I believe that's what the canals were built for when this area was converted from swamp to agriculture land decades ago). There is a pipe that runs from my pool pump, under my backyard, and ends on the canal bank a few inches above the water line, so the system was clearly designed to drain into the canal. I assume this was done with permits and is not uncommon. The South Florida water management agency (runs the canals) would have made a fuss long ago if it was an issue. Of course, we get a letter about once a year saying don't water you lawn with the canal water because they're putting something in it to kill the algae. Probably because there's so much CYA in it from pools! As nasty as that water must be to drink, it's surprising how pretty it is to look at.
As for other comments, OK I now accept that the only clear reason to switch to SWG is convenience. The water quality issues mentioned above can satisfied with proper BBB technique, and use of salts and borates, and I don't expect to save any money on SWG vs BBB. But I'm still strongly considering it for convenience sake. I was paying the pool guy $90x12 a year and that should more than cover the cost of a good SWG system.
