Smaller spa = tougher sanitizer level maintenance?

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B

Baumeister

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Bronze Supporter
Jul 11, 2018
15
Auburn,CA
Hi all,
This is my first real-world experience with spa ownership, a 3-person LifeSmart LS300 from Home Depot. In the first week, I've had a tough time maintaining the chlorine level without overshooting(or it decaying away) to the point that yesterday I purged it with Ahh-some, drained and started over.

It occurred to me that the smaller capacity(260 gallons) would contribute to this, how does everyone deal with this? I'm thinking this is a perfect application for the ControlOMatic SmarterSpa?

Thanks!
Erick
 
B,

You will just drive yourself crazy if you worry about "overshooting" your FC level. There is really no down side to having a little too much FC as long as you stay well below the shock level in this chart... FC/CYA Levels

The key here is to just make sure you never go below the minimum level..

Thanks,

Jim R.
 
Thanks, Jim. I think I'm just surprised by the much faster decay rate. Besides my wife and I, we have a 11 and 13 year old using it randomly, the FC hasn't been too predictable for me yet like I'm used to with pool measurements.
 
Baumeister said:
Thanks, Jim. I think I'm just surprised by the much faster decay rate. Besides my wife and I, we have a 11 and 13 year old using it randomly, the FC hasn't been too predictable for me yet like I'm used to with pool measurements.
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It's a small volume and a lot of waste, so it's a lot different then a pool. For example, your pool is 8600 gallons. Assuming it has the same FC level as the spa, there is 33 times more available chlorine in the pool for breaking down waste. On top of this, a pool is usually much cooler, whereas in a spa you are usually sweating to some extend, and the sweat is waste that needs to be broken down. So this double whammy of much less available chlorine and way more waste means that the FC levels drop very quickly with usage, whereas the pool will be a lot more stable.

My experience is even if the FC level is at the mid to upper end of target for our CYA, and my wife and I soak for an hour or so, by the next day I may have 0 FC left in the spa. What I do, and what I think nearly all spas need, is to add some amount of chlorine immediately on leaving the spa, so that the residual bather waste can be broken down without crashing the FC down to 0.

Depending on how long we soak and what the FC level was before we got in, I may add 2-4 oz of 8.25% bleach immediately after getting out of the spa. Usually that is closer to 4 oz. My personal goal is to add enough on getting out that when I test the next day I'm at or above the minimum FC level. After some trial and error you should find an appropriate amount of chlorine to add on getting out of the spa based on your particular soak lengths and temps.

I would suggest the following, based on my experience:
  1. Test FC every time before entering spa, ensure it is at least at the minimum end of the target range before getting in.
    1. If you are going to soak for an especially long period of time (like 1+ hours), you may want this at the mid to upper target range before getting in.
  2. Get in, enjoy your soak.
  3. On getting out, add X oz of bleach based on soak length and experience.
  4. Test FC the next day. If it is below the minimum, boost it up to the "SLAM" level for your CYA, and add another oz or two to the amount you added in Step #3 the next time you use the spa.
After a couple of soak cycles, you should get a feel for how much to add so that the next day the FC is at or above the minimum level.

Hope this helps!

P.S. Some bather waste takes time to break down, as much as a day or two, maybe even three days after the last use. While the FC will drop rapidly for the first half a day to a day after use, this drop should level off with time. Within a few days of no usage, assuming the FC level is maintained in the target range, you should a very low drop in FC usage, like a couple ppm/day or so, assuming no UV/ozone systems since those attack and destroy FC.
 
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I also find that it helps to open the lid a couple of times a week for half and hour or so. Obviously when the sun is shinning.

I have a small "over the shoulder" SWCG that makes adding additional chlorine something that I rarely have to do...

As mentioned above... after you use the spa for a couple of weeks you kind of get a feel for what it needs.. I only test about once a week.

Thanks,

Jim R.
 
Straight from the horse's mouth -

The rough rule-of-thumb that applies for soaking in a hot (104ºF) spa that has no ozonator is that every person-hour of soaking needs roughly 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach (3-1/2 fluid ounces of 8.25% bleach) or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize bather waste. With an ozonator, the amounts could be roughly cut in half. These quantities are independent of spa size and are the same regardless of whether you use chlorine or are activating bromine from a bromide bank.
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The rule of thumb based on European studies of commercial hot tubs is that you need about 7 grams of chlorine per person-hour of soaking. These studies use the fact that people are sweating, shedding skin and other bodily fluids during a soak.

Do note though that adding chlorine right after soaking will generate a fairly high CC load. Some of those CC's are going to be the organic variety (chlorine reacting with creatinine for example) and those CCs are persistent, ie, they can not be further oxidized by more chlorine. This is why tubs tend to build up CCs overtime and why draining is necessary. One could use ozone or UV oxidation to breakdown organic compounds into simpler forms before adding chlorine and thus reduce the amount of persistent CCs formed, but that would require a setup that is generally more complicated than what one finds in standard hot tub designs.
 
My tub is 240 gallons, similar to yours. Purging the tub with a surfactant and an elevated FC level is important. Watching the amount of biofilm release (off color foam) will determine if you need more than one purge. Once clean and freshly filled bring your CYA up to 30ppm max. You can use dichlor but I find granular CYA in a sock method to be best. Keeping your FC in the zone is critical, never below minimum and not above max for safe soaking. Add FC after every soak. I use 10% and add 1oz per person/ bather. I also add 1/2 oz of 10% on days of no use. Keep tabs on your FC and pH often and check your CYA after several weeks as it degrades faster in hot water.

All that said you will experience a rising CC as the weeks progress and some people are sensative to higher CCs causing skin irritation and itching. To slow the CC rise clean your filter often. Best to have two and swap them out, cleaning them with surfactant and FC in a bucket. Eventually you will need to exchange most of the water and for me that is after six weeks but my tub gets used every day and often twice a day.

This is my experience with a tub similar to yours, happy soaking.
 
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