chem geek said:
First of all, an SWG can't remain algae free with 3 ppm FC with 80 ppm CYA unless the pool is poor in algae nutrients. We've had plenty of examples of a 3 ppm FC target that simply doesn't work -- it's too close to the edge with high chlorine demand even if algae isn't yet visible. 4 ppm FC is pretty much the minimum required with 80 ppm CYA and as a minimum that's a number to be measured in the morning after any overnight loss.
Also, remember that the SWG is maintaining the FC level whenever the pump is running so if things are set up correctly where that is mostly during the day when FC loss is greatest, then the FC level is fairly constant. A manually dosed pool will fluctuate in FC up and down so targeting an "average" 4 ppm FC with 80 ppm CYA may have the FC get below that over long enough periods of time that algae can grow. In theory, an automated dosing system, such as a peristaltic pump, maintaining 4 ppm FC with 80 ppm CYA might work, but we don't have enough experience with those to know for sure.
Also, there is some superchlorination in the SWG itself that might help kill off floating algae though obviously would do nothing against any algae on pool surfaces. The superchlorination in the SWG is different than that from manual dosing using hypochlorite chlorine because the chlorine generated in the SWG at the anode is in very acidic conditions, at least until it meets the water that is very basic/alkaline from the cathode.
JasonLion said:
It isn't the salt that allows the lower FC level, as can be seen by running a pool with salt but no SWG. The current theory is that being able to run at a lower FC level has something to do with the fairly extreme conditions inside the SWG cell, but no one really knows for sure.
I see this section has not been responded to in one year but I thought I would chime in.
new to pools last one 25 years ago. inherited a home near foreclosure that had a pool. chems were used/dichlor.
started there last summer since that is what they left behind.
it had a SWG the beeped all last summer but pool was nice, swam only once.
worked on house all summer/fall/winter/spring..still a on going project expect will be near done by Christmas.
now, have a pump very small leak and found a SWG board burnt up, fleabay bought and replaced to find they did not
have screws holding heat sink at transistors...no wonder why it fried. I believe it is about 15+ years old and still works.
even though I have read this BB or forum for some time I have yet to read anything much about the biology of the sand
filter. chem geek has a lot of info on the chemistry of a pool for sure as do many others here for a while. it rubs off.
thanks.
now to jasons comment;
where no one really knows well it may be where the
filter biology comes in.
sand about ten days after it has been backflushed starts to build up bacteria like a under
water gravel fish tank. it may be
the bacteria that helps eat up some of the dead "
super chlorinated" floating algea. since a pool usually cycles the water
through the filter and chlorinator once or more a day.
it does not mean you do not have to brush your pool from time to time...you still do. otherwise you would not get the floating
algae.
