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Advanced Hot Water Chemistry

September 15th, 2014 by

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Beyond pH and Bromine levels, beyond alkalinity and calcium hardness – what else is there?

Maintaining a healthy hot tub is crucial not only for the users of the spa, to avoid sickness, but also for the integrity of your hot tub spa.

The following article on hot tub water chemistry will focus on 3 important tenets:

1. A Hot Tub is Not a Small Pool.

2. Chemicals behave differently in Hot Water.

3. Spa filters are important to chemistry.

 

1. HOT TUBS ARE NOT SMALL SWIMMING POOLS

Although many spa owners treat their spas and swimming pools the same, using the same test kits and even the same chemical treatments, there is a world of difference between the two. The largest difference is in volume. Easy enough to understand, a spa of 400 gallons is quite a bit smaller than a pool containing 20000 gallons.

The main distinction here is in gallons per bather. When 4 persons slip into a 400 gallon spa, that’s the equivalent of 200 swimmers in a 20000 gallon pool. A radical change in water chemistry occurs when people enter a hot tub. The pH tends to jump up dramatically, and the sanitizer is pummeled. The small cartridge filter, adequately sized for an unused spa, becomes immediately overwhelmed.

Bromine tends to respond better than chlorine in this situation, maintaining more efficacy at higher pH levels than chlorine, but even a high level of bromine is rapidly depleted in the presence of several spa users. This leaves your bathers unprotected from pathogenic microorganisms.

This is why a Hot Tub needs to have additional sanitation methods. Using an Ozonator and a mineral purifier together (in addition to bromine), is the best way to ensure extra protection for a hot tub or spa used by several persons at the same time.

This is also why it is so important for spa users to shower thoroughly before using a hot tub. I know that it’s difficult (if not outright rude) to ask guests to shower before using a spa, but just imagine all of the gunk that is washing off their (and your) body – bacteria, dirt, fungus, feces, oils, urine – to name a few. Not to mention all those chemicals from cosmetics, lotions, hair care products, shampoo and soaps. And your skin pores, opening up in that hot water…

 

2. CHEMICALS BEHAVE DIFFERENTLY IN HOT WATER

As water temperature rises, the viscosity or density of water decreases, and molecular activity increases. Sanitizing agents become hyperactive, and quickly dissipate. Carbonates and bicarbonates, hydrogen and hydroxyl ions, and calcium minerals all ‘fly’ around the water at breakneck speed, combining and separating in bizarre ways, not seen in colder water. Molecules in cold water have a greater atomic bonding, and resist change, whereas in hot water, molecular combinations (not all good) occur much more easily in hot water.

Cold water also holds much more entrained oxygen than hot water, and sound travels faster in cold water. Not much to do with hot tub water chemistry, I just think it’s interesting, that’s all. Everything that is in your hot tub water, every speck of dust, every droplet of bodily fluid, all affect water balance, and contribute to Total Dissolved Solids in a hot tub. It’s another property of hot water that solids break down more easily than in cold water. But they don’t go away, they are simply dissolved in the water.

Pool chemicals are not suitable for spas and hot tubs. Namely because of the labeling and dosages listed. It’s very easy to overdose or under dose a hot tub. Even for those chemicals that may be identical, such as pH up or Alkalinity increaser. Although chemically the same, spa chemicals are produced in finer grades, to dissolve more rapidly.

Other pool chemicals, such as clarifiers and algaecides, are not produced for use in hot water temperatures. They break down more readily in water of higher temperatures, and combine in ways that render them useless. These reasons are why you should not use pool chemicals in your spa or hot tub.

 

3. SPA FILTERS ARE MORE IMPORTANT THAN YOU THINK

You may wonder what the spa filter has to do with hot tub water chemistry, but as the title implies, it’s more important than you may think!

Harkening back to our opening paragraph, when 3 or 4 people jump into a hot tub, it can overwhelm a spa filter. I’m speaking of the pleated filter cartridge that serves to strain out small particles in your hot tub. In most cases, their diminutive size is adequate for a hot tub that is not hosting visitors, but place a few humans in the equation, and it can take hours for it to catch up.

In spas, as in swimming pools, there needs to be a balance of sanitation and filtration. A balance is important, if you will – imagine doing it all with only one of these. If you only had sanitation (and no filtration – stagnant water), you would need a very large amount of sanitizer to keep the water clean and clear. Or – you could do without sanitizer, if you had a filter as big as a house, or circulation of hundreds of gallons of water per minute. But this is impractical, so we rely on a balance.

It doesn’t take long for a small cartridge filter to stop pulling it’s weight around a hot tub or spa. When this happens, much more is required of your sanitizer, or more sanitizer is required, I should say. I know that some of you may be guilty of going years without changing the filter cartridge. Sure you clean it – occasionally, but when was the last time you replaced your spa filter?

For best results, replace your filter cartridge every 10-15 cleanings, or every 12-24 months, depending on how often the spa is used. A spa filter that needs replacement won’t stand up and wave it’s hand for a substitute, it quietly keeps chugging along, allowing microscopic debris to pass through unfiltered.

When your filter is doing less than what is required, your water suffers, and it could affect the health of your spa users and your spa luster. Do yourself a favor and set a calendar reminder to replace your spa filter on a regular basis. Or, do what I do, and buy them in pairs, and alternate cartridges when one is removed for cleaning. This allows me to go 24 months between purchases, and also means that I allow the cartridge to dry fully after cleaning it, which kills any contaminants buried deep inside the fibers.

 

Daniel Lara
Hot Tub Works

 

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