Is main drain necessary?

[JimK]

I appreciate you sharing your experience with this.

I'm wondering how long my SWCG can stay off before CL dips below the minimum? I try not to let it dip below 5ppm with CYA maintained at 70-80ppm, and preferably maintain between 6-7ppm for a little wiggle room.

Am I correct that if right now I have to set the SWCG to 70% for 12 hours, then running at 100% I would have to run it 8.4 hrs (12*.7=8.4)? Am I figuring that right?

[mas985]

Yes, that is correct. As for the FC, just measure it one evening after the sun goes down and see what it is. But at 8 hours, that should still be enough to cover most of the daylight hours anyway.

[JimK]

Thanks.

I was looking up your SWCG and it looks like it uses the same cell, T-15 Turbo Cell, as my Aqua Rite (now Hayward, I believe).

[mas985]

Yes, mine uses the T-15 and currently on my 9th year. It produces about 1.45 lbs of chlorine per 24 hr period at 100%. So in 12 hrs at 70%, that would be about 1/2 lbs per day or about 3 ppm per day added to the pool which would be on the high side. So either your cell is indeed failing or you have something else in the pool that is consuming a lot of chlorine.

Have you done an overnight free chlorine loss test? You should not lose much chlorine overnight and if you do, then it could be something growing in the pool.

[JimK]

Wow, 9 years with the same cell?

Our pool was installed in March 2004 and included the Aqua Rite. In June 2008 the cell died with some warranty left on it. At that time the T-15 cell and controller came with a 5yr pro rated warranty. I've since learned that it likely died prematurely due to using it to shock the pool (long story.....I'll just say I don't use pool store recommendations anymore ). The replacement cell is the one I have now (I learned my lesson and only use it to maintain CL level).

I did wonder if the reason for the higher setting I'm using now was something driving up demand, but my pool passes the overnight test and there's never any CC.

I didn't realize that a 3ppm loss a day was considered on the high side. I'll take a look through my records for times when the SWCG was off to see if I can tell how much I normally lose on a sunny day.

[JimK]

Looking back it seems like 3ppm loss on a sunny day is about normal for my pool. Perhaps this evening and tomorrow morning I'll repeat the overnight test to see if FC is still holding overnight.

On topic, I'm surprised no one else has weighed in on the main drain question.

[JimK]

Checked FC this morning....no FC loss overnight.

Concerning the main drain, it does seem that throttling down flow through the MD has improved skimmer performance. That said, I'm not sure I'd want to be completely without one. There are times during late spring when the trees are dropping a lot of stuff and the skimmers clog up while I'm at work. With the MD there's still water flow preventing damage to the system.

Perhaps during times of lots of debris falling into the pool I'll keep the MD open and close it off the rest of the time.