How long to run filter and SWG

[Phillbo]

I run mine from 9pm to 1am and then again from 5am to 9am. This is primarily due to 9pm to 9am being discounted (read- not gouged) electricity rates. I live in Az so 8 hours min is recommended in order to keep my chlorine level up.

[waterbear]

Pump run time and cell output percentage are inter related. For example a unit set at 10% and running for 1 hour (60 minutes) and a unit running at 100% for 6 minutes would generate the exact same amount of chlorine since both would have the cell on and producing chlorine for a total of 6 minutes. However, the first scenario is going to be more effective at filtering your pool.

So given this (and assuming your unit is NOT undersized for your pool) you first want to adjust your pump run time to provide proper filtration (usually a minimum of 6 hours and possibly as long as 12 hours, depending on your filter/ pump combination and the size of your pool). This can be one continuous run or broken into smaller runs. However, if you break it down find out what the reversal cycle time is for your SWG and make the smaller runs an even multiple of this timespan (for example, my Goldline unit reverses polarity once every 100 minutes, and Pool Pilot units have an adjustable reversal time that defaults to 4 hours, if memory serves me correctly.)

Once you have your pump run time squared away to provide proper filtration you then want to adjust the cell output to maintain the FC level at the desired level ,3-5 ppm FC works well with most SWG installations.

One mistake that many people make with SWGs is NOT having enough CYA in the water. With a SWG you want it at the manufacturers recommended MAXIMUM (usually 80 or 100 ppm depending on the brand). By keeping the CYA at the top of the range you can maintain the FC in the recommended 3-5 ppm (which seems to work out best for a SWG) with the minimum cell on time. This has the desired effect of minimizing the acid demand (pH rise) that is commonly seen with SWGs. ( I won't go into the chemistry behind it here but it is NOT what most people think. It is caused by the outgassing of carbon dioxide, which brings me to the next thing....lowering the TA.)

Finally, to further minimize the acid demand and give you better pH stability, lower the TA to 80 ppm or less and adjust the pH to 7.6. When the pH climbs to 7.8 add enough acid to drop it to 7.6 but not lower since the lower you drop the pH the faster it rises again (once again I won't go into the chemistry but it's because of outgassing of CO2).

One last thing that you can do that I would highly recommend is adding borates to 50 ppm. This does two things (it does more than two but these two have the biggest impact on your SWG operation)

1) it acts as an algaestat and effectively controls nascent algae blooms so you will have a reduced chlorine demand and can dial the output of your generator down even more and still maintain the same FC level. This has the effect of reducing your acid demand even more by causing less outgassing of CO2!
2) It introduces a secondary boric acid/borate pH buffer that works in conjunction with the normal bicarbonate/carbon dioxide buffer (we measure the bicarbonate part of this buffer with the TA test) that effectively "locks" the pH at around 7.6-7.7 for a longer time than without the borates.

I hope you find this useful and hope this has not confused you. If so just ask. Much of the actual chemistry that I alluded to can be found in the "china shop" section of the forum but realize that it is not for the weak of heart! (chemistry nerds tend to hang out there!)