Is main drain necessary?

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.

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.

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.

Just my 2 ¢... I have a 5 1/2' deep end, a 40' long pool, and only a low side-wall drain and skimmer at one end and it does fine without a bottom drain.