Shocks

[John Quincy]

New Spa Owner

350 gallons

Going with Chlorine (Dichlor 1st week and a half or so then bleach depending on CYA levels) (have ordered TS-100 but am using strips until it arrives). Thanks ChemGeek for the suggestions.

My next challenge is which Shock to use. Is it enough to simply bring chlorine levels to 10 ppm fc every 5 or six days (maybe more depending on tests) or do oxidizers offer any significant advantages?

My small town has a couple stores that carry:

Potassium Perymonosulfate - The local pool store is pushing this as shock for bromide users. Is this the same thing as Potassium Monopersulfate? Is there any reason why this cannot be used in a chlorine spa as a shock.

Dupont's Oxone - Dupont's web site states that this is Potassium Perymonosulfate aka Potassium Monopersulfate. See my questions above regarding this shock.

Should I just keep things simple and just shock with chlorine to 10 ppm fc or are there any significant advantages to using oxidizers?

[chem geek]

If you don't measure Combined Chlorine (CC) above 0.5 ppm BEFORE you get in (you'll measure them after you get out since they form while you are in), then you don't need to shock, at least not for removing CCs. If you regularly maintain around 4 ppm FC, then you shouldn't need to shock for sanitation either, but you could play it extra safe giving an extra chlorine dose every now and then. Just be sure and keep the cover off for about an hour after you shock, regardless of what kind of shock you use.

If you find that you get persistent CCs, then you can consider using the monopersulfate (MPS) non-chlorine shock instead, but some people have skin sensitivity to it. It's up to you which way to go: 1) no shocking because CC is low; 2) shock with chlorine; 3) shock with MPS. MPS will oxidize some organics that chlorine has a harder time with so using MPS on occasion is nice, but there's the old adage of "if it ain't broke, don't fix it". Dupont officially says that MPS should be used after every use of the spa so that some residual is there for the next time you get in plus spas have relatively heavier bather loads compared to pools (since there is such a smaller amount of volume). I'm not settled yet on how much MPS should be used or is needed. There are several users doing different things so we'll see what people report as their experiences.

Richard

[John Quincy]

Thanks for clarifying that pre-bodily submersion CC levels determine when to shock and the great summary. All other sources keep bombarding me with using time not actual water quality levels. There are so many conflicting sources that it is hard to keep ones moorings. Many methods may lead to the same overall result but not if you follow them all at the same time.

At the pool supply store, the managers thought it was odd that one would want to use MPS on a non-bromide pool. Instead of MPS, she was suggesting another stabilized chlorine product in addition to dichlor (I think it was a more concetrated form of dichlor). From your reply, this seems more like a matter of what she prefers.

If it will not hurt to use it in a chlorinated spa (from all the posts, it seems like it is fine), I would like to try an oxidizer when necessary:

1) It usually is a good idea to use a multi pronged strategy to deal with waste/pests especially if it is fairly benign.

2) Oxidizing agents should clear from the spa more quickly than chlorine shock allowing one to use the spa sooner.

3) As oxidation is one of our bodies main infection fighting methods, it probably works pretty well in the spa.

You hit the nail on the head when you said desire to add things to the mix needs to be tempered with "if it ain't broke do not fix it." In any case, I doubt that there will never be a time when the CC levels do not get broke (via me neglecting to add chlorine) and oxidizing is a benign alternative to chlorine.

Dupont literature is full of many helpful suggestions (e.g. Do not mix Dupont Spa Care products with those of any other manufacturers." IN BOLD PRINT).

While I am on the subject of "if it aint broke don't fix it", the chemical store also suggested that I add scale preventor on start up and weekly. I guess I should have waited for the TF100 and done a calcium hardness plus ph test first. Beside seeing large deposits on the sides of my tub, what test results would determine if I need a scale preventer?

[chem geek]

MPS is perfectly fine and compatible with both bromine and chlorine. However, it is a rather strong oxidizer and as such some people have skin sensitivity to it. It is NOT a sanitizer. It oxidizes organics and ammonia before chlorine gets a chance to and therefore prevents the formation of Combined Chlorine, but it does not kill pathogens nor prevent algae. If you let your chlorine levels get to zero, you are asking for trouble even if there were MPS still around. So don't think of MPS as helping your sanitation routine except that chlorine may last a bit longer (so you'll need to add less each time) since MPS will be doing most of the oxidizing work leaving chlorine to kill pathogens.

[EDIT] I wrote the following paragraph based on what the store's were telling you in your last post offering Dichlor products -- your first post indicates you plan on switching to bleach. Sorry for the duplicate advice. [END-EDIT]

For chlorine, you should consider not using only Dichlor as that will increase the CYA levels over time. For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm and the CYA does not go away until the next time you drain and refill the spa. Higher levels of CYA reduce chlorine's effectiveness unless you increase the FC proportionately. Roughly speaking, the ratio of FC to CYA determines the amount of actual disinfecting chlorine (hypochlorous acid) in the water (at a given pH). After 1-2 weeks of using Dichlor after an initial fill of water, you can then switch to using unscented bleach such as 6% Clorox Regular or an off-brand Ultra bleach. To raise the FC by 4 ppm in 350 gallons it takes 2 teaspoons of Dichlor or 3 fluid ounces (6 tablespoons) of 6% bleach.

As for scale prevention, this is unlikely unless you use well water, but you can always check the water quality report from your water utility as that will tell you the Total Hardness level and might even tell you the Calcium Hardness. If they only tell you Total Hardness, then divide that by 1.6 to roughly get the Calcium Hardness for typical waters.

Richard