Are My Dealer's Chemical Guidelines Reasonable?

[ht2020]

I'm a bit confused about my dealer's chemical guidelines. They are using Leisure Time products: Here are their instructions:

Before each Use: Add 1-2 oz of Renew (I think this is MPS)

After each Use: Add 1/2 -2oz of Chlorine

Weekly: Add 2 oz of Defender (I can't tell if this increases or decreases calcium hardness)

Add 2-5oz of Renew depending on weekly use

Use Test Strip to determine whether any adjustment to chlorine, PH or Alkalinity is necessary

I'm not understanding why the extensive shocking with MPS? My understanding was that shocking is done in conjunction with heavy use, high bather load, high temperatures etc. According to these instructions I would be shocking the spa every day.

The hot springs manual suggests "a weekly or monthly super chlorination 1.5 tsp dichlor/250 gal or double that amount for a shock". Incidentally, the hotsprings manual also advises against using bleach or muriatic acid.

[chem geek]

You should be able to just add chlorine after each use proportional to your bather load if you use the tub every day or two. If you don't use the tub for some days, then you need to add more chlorine in between your tub usage days. If you add the proper amount of chlorine, you shouldn't need to use non-chlorine shock (MPS) nor should you need to shock your tub. However, if you use only Dichlor, then the Cyanuric Acid (CYA) level will build up making the chlorine less effective over time. You would then need to change your water sooner. If you were to use the Dichlor-then-bleach method, then you'd be able to go at least twice as long before changing the water.

With no ozonator, every person-hour of soaking in a hot (104ºF) spa 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). With an ozonator, the amounts may be half or less. The 1/2 to 2 ounces (that's 3 to 12 teaspoons) they recommend for Dichlor after each soak sounds high unless you've got 1-4 people soaking for an hour.

The reason they say not to add bleach is that if you use bleach without any CYA in the water then the chlorine level is too strong and damaging. However, if you have CYA in the water first, this is not a problem. That's why it's the Dichlor-then-bleach method though technically one could start out adding pure CYA first, but CYA is slow to dissolve so using Dichlor as your chlorine source is convenient and for every 10 ppm Free Chlorine (FC) it also increases CYA by 9 ppm.

If you do decide to go with Dichlor-then-bleach, then there are additional things you need to do such as lowering the Total Alkalinity (TA) level to 50 ppm and adding 50 ppm borates (usually from boric acid). That's another reason the manufacturer doesn't recommend bleach which is that without these other adjustments a higher TA level would cause more carbon dioxide outgassing having the pH rise and that could cause scaling depending on your Calcium Hardness (CH) level. Dichlor is net acidic when accounting for chlorine usage/consumption which is acidic.

[Spa_Guru]

It is amazing even after all this time the ignorance of dealers and salespeople on water chemistry.

But then most of their information comes from companies whose mission is to sell chemicals.

[Jake the dog man]

I honestly feel that people would do better just starting with a basic chlorine program and only get into all the other stuff on an "as needed" basis. People may mean well, but most people can own a hot tub for years without ever needing much more then chlorine, some test strips & a good dealer.

[ht2020]

Actually, I just happened to read the manual that came with my silver sanitizer (freshwater Ag) and it gives a recipe for "Low Chlorine maintenance". In that recipe it also confirms daily use of MPS before and after using the tub. It also references a test strip to test for MPS level (although the test strip I received from the dealer does not test for MPS). This makes things really confusing as it is totally different than what Watkins advises or than what people on this forum are doing.

[chem geek]

What you are describing is equivalent to the Nature2 system which also uses silver ions with MPS. It's a mostly non-chlorine method and is approved by the EPA for spa disinfection. And yes, the MPS level is measured with test strips (they are OK for that purpose). We do say that this is a reasonable alternative if you don't want to use chlorine. It's more expensive and MPS can be irritating to some though the silver ions break down the most irritating minor component. Note that just as with the chlorine method you still need to add the oxidizer (MPS) in between soaks as it won't usually last for an entire week, but it doesn't drop as fast as chlorine in between soaks and is immune from breakdown from ozone if you have an ozonator.

[ht2020]

So after extensive reading I'm beginning to realize that my dealer is advocating a hybrid system using the Nature2 MPS PLUS adding chlorine . The spa has both the silver sanitizer and an ozonator. The dealer wants me to use MPS (Renew) every day before use, and chlorine after use. Interestingly, the test strips that he provided do not have any ability to test MPS levels. I will need to obtain a second test strip to make sure that MPS is at proper levels. I guess I will need to experiment with the amount of MPS and chlorine that I am using. One thing, however, that I have figured out is that this type of system allows for lower levels of FC (perhaps as low as 1ppm). I will probably aim for 2-3 ppm to play it safe.

[chem geek]

But his system doesn't make much sense. If you are going to spend the extra money on the silver cartridges and MPS, then why not use them and only dose with chlorine "as needed" which is usually every week or so? That we you have no chlorine, not just low chlorine, during most of the week. I don't get it. You usually go one way or the other.

[ht2020]

I'm not sure what the reasoning is. As far as I'm concerned I don't care about how much a particular system costs; I'll do whatever is safest and easiest. Also, I really don't have anything against chlrorine and have happily encountered it in many swimming pools over my lifetime. To me it makes sense to have as many safeguards as possible ie: ozonator, silver sanitizer etc. However, I see your point about the redundancy of his system. I'll use it until my next fill and then I'll try the dichlor then bleach method.

[Hex92]

This is what I do for my 400 gallon tub with ozonator. My wife and I are the only ones who use it.

New fill:

1.5 oz spa-prestart

adjust Calcium

adjust alkalinity and pH with baking soda and pH up

Then:

1 oz of MPS and 1 oz of dichlor every 3-4 days depending on use. (My plan has always been alternate between the 2 every 2 days....but that rarely happens)

Check tub chemistry once a week. Adjust alkalinity and pH as needed.

Change water every 3 months.

Been working fine for 3+ years. Before that we put all kinds of stuff in there that the dealer suggested.

[ht2020]

This is what I do for my 400 gallon tub with ozonator. My wife and I are the only ones who use it.

New fill:

1.5 oz spa-prestart

adjust Calcium

adjust alkalinity and pH with baking soda and pH up

Then:

1 oz of MPS and 1 oz of dichlor every 3-4 days depending on use. (My plan has always been alternate between the 2 every 2 days....but that rarely happens)

Check tub chemistry once a week. Adjust alkalinity and pH as needed.

Change water every 3 months.

Been working fine for 3+ years. Before that we put all kinds of stuff in there that the dealer suggested.

That's interesting. That's pretty close to what my dealer has advised (a hybrid type system). Mine goes one step further in the sense that there's a silver stick involved also. Anyway, it makes me feel better that the system is working well for you. The only downside is I definitely don't want to be changing water every 3 months (I was hoping to stretch that out if possible). One advantage of a low chlorine system is that there's not as much accumulation of combined chlorines and CYA. Therefore, even though daily MPS is more expensive (as chem geek pointed out), it may mean fewer changes over time.

[chem geek]

If you were to use chlorine with no CYA in it, then that is a way of avoiding the CYA buildup. That's what the Dichlor-then-bleach method does since the bleach does not have any CYA in it and people generally find they can go at least twice as long between water changes compared with Dichlor-only.

Just remember that MPS used by itself (with silver ions so you get disinfection) won't keep the water clear over time. It oxidizes some different things than chlorine and some in common. For the common ones, it will prevent formation of those combined chlorine products as you point out. So again, I don't understand why you'd want to use chlorine more frequently than needed if your purpose is to avoid CYA buildup and CCs. You can certainly try adding chlorine once a week and if that's not enough then you can add it more frequently, but usually MPS during the week and chlorine once a week is enough to keep the water clear. Read the Nature2 Manual for the low-chlorine recipe.

As for how long before changing the water, with Dichlor-only the standard Water Replacement Interval (WRI) roughly applies:

WRI (days) = (1/9) * (Spa Size in U.S. Gallons) / (Person-Hours Per Day)

The original formula used "1/3" but presumed 20 minute soaks. So for a 350 gallon spa to last 3 months you could have one person soak for 25 minutes every day using Dichlor-only. If you used Dichlor-then-bleach, then that same level of usage may last 6 months or more. You'll have to let us know how long things last using MPS with chlorine as needed. Just let us know the frequency of your usage.

[Hex92]

In the summer, when we use the spa less, I can go 4 months without changing the water. During the colder months we are in it more, 3 months is about right.

I can tell it needs to be changed when it becomes harder to balance alkalinity/pH. When I start having to add somthing every time I check it I know its time for a change...

And that usually works out to be around 3 months.