Didn't realize my spa water chemistry drifts that fast from the pool

Started by Karen Delgado · · 3 replies
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#1
Ran a test on the spa separate from the pool this week just to check, usually I just test the pool and figure it's close enough since it's attached. Not even close. FC was half what the pool read and pH was up near 8. Same water, same filter, same everything, just sitting there heating and getting jet action a few times a week does something to it. Been treating it as one body of water for two years apparently wrong. Now I'm testing both separately before I add anything. Feel dumb about it honestly, seems obvious in hindsight but nobody tells you that when you get an attached spa, they just say one pump one filter like it's all the same water forever.

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#2
Don't feel dumb, the jets aerating constantly plus the higher heat will off gas chlorine and push pH up way faster than the main pool, I don't have an attached spa but I saw the same pattern with my sun shelf early on, shallower warmer water with more surface agitation just doesn't hold chemistry the same as the deep end. Testing separately before dosing is the right call, you're not wrong in hindsight, the "one pump one filter" framing just glosses over the fact that heat and aeration are doing real work on that water.
#3
no attached spa here so i'm just going off what priya said about the aeration/heat thing, but before i'd even guess what's going on, is your spa on a separate valve you can actually shut off from the pool loop or is it true shared water moving back and forth the whole time? cause if its properly isolated when the jets kick on that's a totally different animal than if its always mixing a little even when it's "off"

that changes whether i'd trust two separate test results as two separate bodies of water or if its more like one pool with a weird corner that heats up faster. kind of curious myself since i might end up with a spa setup someday and this is good to know before i get there
#4
Heat's the bigger driver than aeration, pH up near 8 in the spa screams off gassing from the higher temp, mine does the same thing if I run the spa a few hours straight. Separate valve matters less than you'd think, even shared loop water chemistries different the second it sits hot with jets going.