specifying (sizing) an SWG for a big pool

in-two

Well-known member
Nov 13, 2011
51
Sabina, Italy
Hi Everybody,
Just opened my pool here in central Italy, all good so far but I'm seriously thinking of going over to the 'salty side', not just because of the huge pile of empty bleach jugs but because the pool is at our holiday home and I'm not there the whole time. Our neighbour and local farmer who maintains the pool in our absence was unfortunately partially digested by his tractor (he's getting better, but his arm was broken in three places) isn't up to it and won't be for some time, so a bit of automation is in order. The only SWG units I can easily get here are Zenith and Autochlor, I like the look of the Autochlor units and they come in sizes much bigger than Zenith. The Autochlor unit max outputs are specified in grams of chlorine gas per hour and using their website calculator I get results of between 50 and 92 g/hr, depending on what chlorine level I want, these are the top end of the Autochlor residential range and yet the biggest one (92 g/hr) will only generate 3ppm chlorine with my pool size (160 m3, 42000 galls), according to the calculator. I generally aim for 3-5ppm FC when the pool is stable
On the other hand the retailer states that the 50g/hr unit is big enough for a 230 m3 pool. So, my question (finally) what is the right way to determine the size (output) of an SWG and what factors need to be calculated in?
I get the feeling from reading as much as I can find on TFP that over-sizing is much better than undersizing and that manual bleach addition will always be required in special circumstances, as well as a higher level of CYA than I am used to running (30ppm).
Thanks in advance if you can help out.
In-Two
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
The higher CYA level used with a SWG will cut down your daily FC requirement significantly, presumably to less than 2 ppm/day at the peak of the summer. Ideally you want something that can produce that in no more than 8 hours of run time, which for you pool works out something like 1000 g/day or 41 g/hour. We then recommend getting something two or three times that size for additional safety margin.

Assuming I haven't make any math errors, a 92 g/hr unit should be fine for your pool.
 

in-two

Well-known member
Nov 13, 2011
51
Sabina, Italy
Thanks for speedy and useful response, all I have to do now is save up the 3000 euro for the unit and try to convince my wife that it's part of our neighbour's therapy and not just anew toy...