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Author Topic: Maintaining water quality - Is it easier with more gallons for a given user load  (Read 2156 times)

n.one.one

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I'm not making any decision based on this, it's just a curiosity question for discussion.

Is it easier to maintain water quality with more gallons for a given user load? Let's assume that a couple will use the spa five days per week for 1/2 hour per session which would total five user hours per week. Would it be easier to maintain water quality/chemistry with a 300 or 500 gallon spa? Assume that both spa sizes would be comfortable and affordable for the couple and the only question is maintaining water quality.

My guess is that the larger spa would be better able to handle the user load and would get back to normal more quickly after each use. Any thoughts?
« Last Edit: December 29, 2015, 11:47:47 pm by n.one.one »

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chem geek

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It depends somewhat on how you maintain the water.  If you use Dichlor-only then yes having a larger spa volume has the water last longer because the amount of Dichlor needed for regular heavy bather load (i.e. soaking every day) is related to that bather load and not to the water volume, but the rate of Cyanuric Acid (CYA) concentration buildup is faster in a smaller volume of water.  So the chlorine becomes less effective due to the higher CYA sooner in a smaller tub.

If you were to use the Dichlor-then-bleach method to avoid the CYA buildup, then the buildup is about organic waste that isn't fully oxidized and to a buildup of salt.  So here again a larger tub has the water last longer, but you'll be at least double the time compared to Dichlor-only so the spa volume difference may not matter so much.

The other factor is that in a larger volume of water the chlorine you add after a soak won't have the FC rise as high.  So there will be less wasted chlorine from outgassing.  Also, any errors in dosing don't result in as much change in water values.

So yes, overall, a larger volume of water can be easier to maintain.
« Last Edit: January 02, 2016, 03:59:49 pm by chem geek »

n.one.one

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Thanks chem geek.
I'm a newbie here but have already learned from many of the answers you have provided on other topics.

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