Spas any different?????

[dansdad]

Just wondering if spas because of their heat are tested differently. I have a 400 gallon spa and it sure doesn't take much BBB

[chem geek]

You operate a spa similar to a pool with BBB and the testing is the same, but there are some differences to note. The main one is that due to the higher temperatures and increased aeration from spa jets, the pH tends to rise quickly in spas if you don't significantly lower the Total Alkalinity (TA) level and use supplemental pH buffering. I recommend lowering the TA to 50 ppm (this assumes a CYA level of around 30-40 ppm) and you use 50 ppm Borates (such as from boric acid) in the spa. You can also target a 7.7 or 7.8 pH if that is more stable.

Just note that spas can go bad a lot faster than pools because if the chlorine gets to near zero then bacteria can grow quickly at the hot temperatures and form biofilms that are much more resistant to chlorine.

Another big difference between a residential spa vs. a residential pool is the bather load. Because of the small spa volume, most chlorine usage in a spa used every day or two will be in oxidizing bather waste so proportional to bather load. In between soaks, chlorine demand is usually around 25% of the FC level if there is no ozonator and assuming the spa water is hot. With an ozonator, this demand can increase to 50% or more if a spa is infrequently used (say, only on weekends) since ozone reacts with chlorine. This is why ozonators only make sense in more heavily used spas -- those used every day or two -- since the ozone can then oxidize bather waste and reduce chlorine demand usually by around 50%.

Finally, you have already noted the far lower amounts of chemicals needed due to the small water volume.

[dansdad]

thanks for responding C Geek, Im also putting in 2 tabs of a product called renew to help balance or so the dist. told me. We only have 2 bathers anymore but used by my wife almost daily

[chem geek]

Renew tabs are bromine tabs so you have a bromine spa, not a chlorine spa. That's fine if that's what you want. You may need to shock with chlorine every one or two weeks to keep the water clear. The advantage of using bromine tabs is that it doses your spa with a background dose of bromine so you don't need to dose in between soaks. However, if you have at least one person using the spa every day or two, then you could have a chlorine spa instead. The downside with a chlorine spa is that it needs dosing every day or two, but if you use the spa that frequently then you just dose after each soak. Up to you.

For a chlorine spa, you start of using Dichlor initially until you build up the CYA level to 30-40 ppm and thereafter switch to using regular unscented bleach (NOT splash-less or outdoor).

[dansdad]

C Geek, I use a vision Cartridge. could change to chlorine. Don't really care its what I have always done. I just dumped and refilled 2 days ago and haven't done sanitizing yet. Should I just pay attention to ph?

[chem geek]

The Vision cartridge adds silver ions to the spa, similar to the Nature2 system. The main reason to have that is if you wanted a non-chlorine, non-bromine system where you would instead use non-chlorine shock (43% MPS) as your primary disinfectant/oxidizer in conjunction with the silver. I suppose the silver could be an insurance policy for you if you use a chlorine system in case the chlorine gets too low -- but no guarantee. You'd still need to shock with chlorine once every week or two since MPS alone doesn't handle all that is needed to get rid of bather waste.

So you've got 3 choices -- Silver/MPS, chlorine, bromine.

Why don't we start with chlorine since it's easy to switch from that to silver/MPS and from either of these to bromine. You can't easily switch away from bromine without a water change.

I would lower your Total Alkalinity (TA) to 50 ppm through a process of acid addition and aeration (running the jets) at low pH as described in this HOWTO post. With a chlorine system when you are using bleach the pH would tend to rise due to carbon dioxide outgassing so lowering the TA level minimizes this by essentially driving out that carbon dioxide sooner and not adding it back.

Then I would add 50 ppm Borates from Boric Acid you can get from The Chemistry Store or from AAA Chemicals. You can use The Pool Calculator to calculate dosing. For a 350 gallon you need 13 ounces weight (about 14 ounces volume) of boric acid. This chemical acts as an additional pH buffer that doesn't cause the pH to rise.

Then you use Dichlor as your initial source of chlorine unless you have some Cyanuric Acid (CYA) handy in which case you can try and dissolve 30-40 ppm in a small sock or panty hose you hang over a circulation return flow in the spa and periodically squeeze it. If you use Dichlor, then you use it until you've added 33-44 ppm FC cumulatively and then you switch to bleach (or chlorinating liquid if you have that for the pool already).

The amount of oxidizer you need to add after your soak for every person-hour of soaking (so scale accordingly) and which is independent of spa size is 3-1/2 teaspoons of Dichlor of 5 fluid ounces of 6% bleach or 3-1/2 fluid ounces of 8.25% bleach. The real rule is to add whatever you need so that you measure 1-2 ppm FC at the start of your next soak (you can start out higher, but most people don't like to smell the chlorine or its byproducts during their soak -- if you are soaking with strangers then you can bump up your starting FC at the start of your soak if you like). These amounts assume you have no ozonator. With an ozonator, the chlorine demand is roughly doubled between soaks when not soaking every day (i.e. the background chlorine demand doubles) while the chlorine demand from bather load is roughly cut in half.

As you can see, the chlorine approach is the most complicated, though not too bad once you get the hang of it. It's the least expensive approach since bromine and MPS are more expensive. Many people find the faint chlorine smell less objectionable than bromine (and bromamine). The MPS shouldn't have any odor at all.

For the silver/MPS approach, you don't have to lower the TA much below 80 ppm because the MPS is acidic so instead the TA will drop over time and the pH may drop so you may need to add baking soda on occasion to raise the pH and possibly add something such as 20 Mule Team Borax to raise the pH (though ideally you have the TA at a level where the pH is relatively stable). The 50 ppm borates using boric acid is optional and if used it will stabilize the pH so you don't have to adjust it as frequently. The amount of MPS you need to add after your soak for every person-hour of soaking is 7 teaspoons. Again, the real rule is to have an "OK" level of MPS on the MPS test strips (yes, you'd need to get those if you go with this system).

[dansdad]

Thank you soo much!!!!!!