Water Conditioning & Purification Magazine

Squeaky Clean Spas Without the Chemicals

By C.F. Chubb Michaud CWS-VI

It was Plato who first said, “Necessity is the Mother of Invention.” Inventions come in three stages: discovery, development and evolution. Like many discoveries, most are unintended or accidental.

Granted, the internal combustion engine was not accidental but the combustibility of petroleum probably was as was the observation that gasses expand when heated. Goodyear’s discovery of the vulcanization of rubber is a famed accidental discovery.

Discoveries often occur when the ‘inventor’ is really trying to do something intentionally but observes something else going on and investigates that. Powers of observation do, indeed, play a key role when the obvious is not so obvious.

Some history
Years ago, my chronic back problems prompted my family doctor to prescribe a health spa membership for me, stating that long, hot soaks followed by stretching exercises would relieve the muscle spasms in my back. Better yet, the cost of membership would be partially subsidized by the US government by way of a medical deduction on my 1040.

I did the next best thing… I bought a hot tub. My tub was a bargain. It was delivered on the back of someone’s pickup truck and I never bothered to have a cover fabricated for it (I didn’t know one was supposed to keep them covered).

After I got it installed and wired in, I filled it with a mixture of hard and soft water and followed the directions for chemical treatment and cleaning to a tee. I tested the water every day for the first month. I added chlorine, cyanuric acid, soda ash, shock treated it, coagulated it, filtered it and then added more chlorine. If you missed a day or two, you paid for it with the frog-pond odor and slippery walls.

Being open to the atmosphere (and we have lots of that in Los Angeles) it was also open to the birds and bees (requiring more chlorine). A very messy bottlebrush tree in my back yard seemed to be able to drop every leaf into my tub. (OK…more chlorine and some new filters).

Evaporative losses required more water! OMG…TDS over 3,500! The water smelled like a public restroom that had just been cleaned with a bucket of bleach. (Maybe the health club membership would have been the better option.)


What You Need To Go Chemical Free
First, you need access to take water out and put water back. Drop lines will work with the pump and filters located external to the spa. You will not be able to simply tap a PVC pipe to pull water out and return it to the same pipe without a check valve in between the two ports (see illustration below).

I found a reliable pump with magnetic drive and good temperature tolerance. I also discovered a strainer with a blow-down valve, halfinch FNPT in/out and an 80-mesh screen.

The sediment filter is five-micron melt blown and the magic media cartridge is one pound (0.45 kg) per 100 gallons (379 L). Without the solar panel, you will need a total of four, half-inch ball valves plus a mounting bracket for the filters. Good luck!


Plenum problems
Hot tubs in those days (1980s) had a plenum chamber under the seats and floor. When you wanted to make the tub ‘boil’, you turned on a very noisy blower that forced air into the plenum chamber and the tub came alive with turbulence.

The thing is, when you turned off the blower, the plenum chambers refilled with the same water that was in the tub and it carried with it all the things necessary to support life (body oils, soap, dirt, skin cells, bacteria and anything else the birds and bees decided to drop in that day). These chambers did not get re-circulated with the regular filtration functions. If you didn’t use the tub for a few weeks, things happened.

Once I came home from a field trip and decided to fire up the tub for a relaxing soak. I brought it up to temperature and kicked on the blower. The plenum chambers then decided to extrude these long strands of black and green ‘spaghetti’ that had been growing in the warm, dark, nutrient rich, deoxygenated waters of its incubators!

The next day, I drained the tub, refilled it and added a pint of liquid chlorine. Then I turned on the blowers, emptied the plenums and refilled them with super chlorinated water.

After sitting a few hours, I blew this water out along with more spaghetti and drained it again. I probably had to repeat this three times. After the final refill, I threw three hockey puck sized chlorine tablets into the skimmer and let it all re-circulate for two days. After three days, the smell of chlorine was so strong, I didn’t dare use it.

Tests confirmed the chlorine was somewhere over 10 ppm. But the water was clear and there was no more spaghetti when it turned on the air blower. This was no fun. I began to think that perhaps if I drained it every other day and only used it once or twice a week I might keep up with it.

Naaah, there’s got to be a better way. (It still hadn’t occurred to me to put a cover over the tub).

I made up a filter at work to reduce the chlorine. It was a crude ‘pipe bomb’ made with three-inch PVC, some screen, a lot of reducer fittings and a couple of pounds of granular activated carbon. I thought I could keep the chlorine high between uses, utilizing this little filter with a separate recirculation pump to bring it down when I wanted to use the tub. Of course, I would have to plan in advance.

To simplify things, I programmed the de-chlorinator to turn on for about three hours every afternoon and the tub to start its main filter and heater around 6:00 PM. By 9:00 PM, I had a hot tub and no chlorine.

If I used the tub, I had to do a small shock-treat with a tablespoon of granular chlorine. If I didn’t use the tub, I still had to remember to add chlorine. Otherwise….spaghetti factory!

The invention
I limped along with this arrangement for six months or so, then decided to go high tech. I replaced the three-inch ‘pipe bomb’ carbon filter with a 10-inch media cartridge containing about two and one-half pounds of filtration media.

I then got called out of town on a business trip without giving written instructions to ‘whom it may concern’ about proper care of the tub. I returned home five days later and wondered what shape the tub would be in as I drove home. The little de-chlorinator would surely be doing its job but I didn’t have an automated re-chlorinator. I didn’t go near it that evening but decided to tackle it the next morning.

The discovery
Prepared for the worst, I walked out onto the deck to check the tub. Hmmm. The water was pristine aside from the few feathers from errant birds.

I turned on the blower. Hmmmm… no spaghetti. I also noted that with the blower on there was neither frog pond nor chlorine odor. I skimmed off a few floaties, added water and walked away.

I continued to observe the tub for a few more weeks with frequent uses. I added no additional chlorine. I added neither cyanuric acid nor soda ash. The pH seemed stable at around 8.2. The alkalinity was in the 180-ppm range and hardness stayed at around five grains (I added only softened water for makeup) although the TDS had risen to around 1000 ppm. I finally fashioned a cover for the tub made from bubble wrap that really cut down on the feathers.

The only maintenance I had to do was clean the main filters every six months and check on my little media filter. Five and a half years later while on a family vacation, my little recirculation pump failed and I came home to a familiar sight. I had to clean things up and replace the pump.

The development
This time I made the changes permanent with hard wiring and hard plumbing. The thing is I had gone six years without adding any chemicals and without changing the water. I even had plate counts run on the spa water (notice I now call it a spa and not a tub) and the results were negative (a good thing) each time.

On occasion, I would pump off 50 gallons (189 L) or so of the old water and replace it with soft water. The TDS stayed under 2000 and the spa stayed squeaky clean without the use of any chemicals.

I have also built a half dozen of these for friends to try. All report very positive results and no chemicals used.

Fast forward
A few years ago I did some major remodeling on my home and deck. In the process, my tub accidentally got knocked over the rail from the second floor deck, fell onto a wheelbarrow and cracked. I replaced it with a more modern and larger spa.

The new one did not have those troublesome plenum chambers but used a Venturi for the air action. I also ordered a few added fittings to accommodate my filter …and this one came with an attractive insulated cover!

I filled it and on day one, I hooked up a new media filter with a reliable three-to-five gpm pump, all hard wired in and on its own timer. I also plumbed in a solar panel that runs off the same pump.

Between 10:00 AM and 2:30 PM, the pump turns on, draws water from the bottom of the spa, circulates it to the media filter and then to the solar panel and back to the top of the spa. The main filter operates four times a day for one half hour each time (heavier usage might dictate more filtration). Now, I not only have a chemical-free spa but I don’t have to heat it electrically.

Spa maintenance
Chemical free does not mean maintenance free. Hot tubs and spas are very different than pools. Five people using a 300-gallon (1,136 L) spa is equivalent to 500 people crammed into a 30,000 gallon (113,562 L) pool!

Temperatures in a spa are maintained at over 100 oF (38 oC). Evaporative losses are higher and conditions are very conducive to defoliating skin and extracting body oils and salts.

Over time, spas load up with soap, lotions, oils, salts, skin cells, hair, soluble proteins (think pot roast), dirt, fabric softener, soap scum, lint and bacteria (dead or alive). Some people use their spas as bathtubs. Kids may use them in ways we don’t want to imagine (think aquarium).

Filters only remove particulate but you have to address solubles as well. Spa manufacturers stress filtration, filtration, filtration.

Eventually one can observe a change in clarity and surface tension of the water (there will be a tendency for the water to form lingering foam when aerated). Once a month I perform a maintenance trick I call ‘semi-automatic semi-dissolved air floatation filtration.’ I turn the main pump on high, open all the jets and turn on the aerator.

As the micro-bubbles pop to the surface, they carry with them oils and particulates that get trapped in the foam and migrate to the main skimmer. Small bubbles coalesce into larger ones and form gel-like foam.

The foam will be brownish in color. I simply skim the foam off with a leaf skimmer. When the water is clean, the bubbles pop as soon as they reach the surface. No more foam. No more dirt.

Evolution
Year’s back, I spoke with a few spa manufacturers about the media cartridge idea. Basically, I was told ‘if it ain’t broke, don’t fix it.’ They explained that they already had good systems in place that were working well (all chemical), the cartridge idea would be a difficult retro-fit and public spas (those at local swimming pools, the Y, health clubs, hotels, resorts, country clubs, etc) actually require a chlorine residual.

Besides, it would put their local pool and spa service guys out of work. That was the end of the Evolution.

So this information is being offered to all of those ‘wanna be’ do-it-yourselfers out there who own a hot tub or have friends with same who want to shake the chlorine habit and automate their spa maintenance.

Enjoy!

About the Products
A KDF® filter with KDF55 filtration material was used in developing this solution, as was a Little Giant Model 4-MD-SC in 115V AC with 1/10 HP motor pump and a Ron-Vik strainer.

 

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