Water exchange between hot tub and pool.

Gibby13

Well-known member
Jul 12, 2019
94
Elgin, SC
Both our pool and hot tub are SWG. If I was thinking ahead more, I would have got a different Pentair unit to control both. Maybe in the future I'll upgrade.

I have refilled the hot tub ever 3 months or so, sometimes sooner.

So I was wondering, since I never drain and refill the pool on a schedule just after lots of rain. And to not lose chemicals, any reason not to drain the hot tub into the pool and refill the hot tub from the pool?

Pro's and Con's would be nice. Thanks!
 

jimmythegreek

TFP Expert
Bronze Supporter
In The Industry
Aug 10, 2017
3,058
Morris Cnty NJ
Are we talking a standalone spa or an integrated pool/spa?

I dont drain into the pool because I ahhsome purge the tub every 3mos or so when its time to change water. If I need to repair or get rid of normal water i will drain into the pool if it's on low side. I do fill the tub from the pool in warmer seasons but only halfway at the most. Reason is I dont want my CYA that high in the tub. The rest I fill from the hose spigot on house water
 

Gibby13

Well-known member
Jul 12, 2019
94
Elgin, SC
What is the chemistry levels of the spa water when you would drain it to the pool? Why are you draining the spa water?
The filter doesn't seem like it can keep up and gets a little foamy. Aslo, I have been doing a SLAM for 13 days and can't get the CC below 2. Even when I initially fill it, it starts around 0.5.

Are we talking a standalone spa or an integrated pool/spa?

I dont drain into the pool because I ahhsome purge the tub every 3mos or so when its time to change water. If I need to repair or get rid of normal water i will drain into the pool if it's on low side. I do fill the tub from the pool in warmer seasons but only halfway at the most. Reason is I dont want my CYA that high in the tub. The rest I fill from the hose spigot on house water
Standalone. Why don't you want the CYA as high in the spa?
 

Newdude

Well-known member
Jun 16, 2019
4,795
NY
CYA in hot tubs is generally just for swimmer comfort. You need some to make the chlorine less harsh on the skin. So we shoot for the low end range of a chlorine pool. Even if you use yours during the day sometimes, the sun won’t burn off nearly as much FC as it does in the pool uncovered all day every day. For most people the hot tub is only used in the late afternoon or evening (after work), when the sun burn off doesn’t matter
 

Newdude

Well-known member
Jun 16, 2019
4,795
NY
In regards to the CYA above, it’s just the CYA that’s kept in the low range of the FC/CYA Chart. The FC on the other hand should be kept in the higher range due to the ‘heavy swimmer load’ that is the nature of a hot tub. One person in the 500 gallon hot tub is the equivalent of 20 people in a 10k gallon pool. If you have 3 people enjoying the tub it’s like 60 people in a 10k gal pool. So you have to expect to use the FC much faster in a hot tub during use and bring it up to SLAM levels after use to kill all the residual organic matter you left behind.