Spa Sanitation

[Dibbler]

Hi,

Can someone clarify please as I have conflicting info (unsurprisingly) between spa supplier and TFP wisdom.

I have a 1800L Standalone Spa, with an Ozone generator(uncontrollable so I assume always on) supplier has advised to add 1 Tblspn of Shock(MPS) after use, more if heavy load and once a week 1 Tblspn of Chlorine (Lithium Hypo).

Water is generally clear, occasional use of floc, filter runs for 4 hours overnight, SetTemp 38DegC

Now this conflicts with accepted TFP wisdom over the use of Chlorine in Spas, my ozone eats the FC as is expected, My gut feel is I should be following TFP FC rules, how can a supplier get it so wrong? And more importantly how do I easily manage FC with ozone?

Thanks
Simon

 

[chem geek]

The supplier is assuming that there is enough ozone that the spa remains safe even when the chlorine goes to near-zero which it does because ozone consumes chlorine (something the supplier probably denies or does not realize is the case). It is possible that the ozonator is on frequently enough and is powerful enough to leave a residual of ozone in the bulk spa water long enough for disinfection, but in that case it will also likely be outgassing and degrading the hot tub cover and being harsh on other spa components. If the ozonator isn't that powerful or on that long, then there is less wear-and-tear, but also less disinfection and more risk of the spa water and surfaces going south with bacterial growth.

As for how to manage the chlorine given the ozone, it's not easy unless you use the spa or dose frequently. If you use the spa every day or two, you just add enough chlorine after each soak so that you at least have a small residual of 1-2 ppm FC at the start of your next soak (assuming you don't want to soak with higher chlorine levels). However, if you only use the spa on weekends, then you'd need to dose additionally during the week to keep the chlorine level at a reasonable level.

This is why some people use bromine since setting up a bromide bank allows for the ozone to convert bromide to bromine. With enough ozone, you may not need to have bromine tabs in a floating feeder. You would need to use additional oxidizer after a soak for heavier bather loads. Note that a bromine spa smells different than a chlorine one and some people prefer one over the other (most prefer chlorine).

 

[Dibbler]

Thanks Richard, as usual they are good at selling things but not so good at the chemistry or the theory it seems.
I'll add the Lithium Hypo after use and in between if not used, check to ensure a FC of 1-2ppm after a couple of days and adjust accordingly.
Is there any point wasting my time with the MPS if I'm using the Hypo?
Given that its covered most of the time is there any benefit in maintaining a very low level of CYA just to offset the Chlorine harshness a little?
On balance I don't think I want to bother with Bromine, just something else to confuse me.

 

[chem geek]

You most definitely want to build up (say, via Dichlor) or add CYA to the water to reduce chlorine's active strength so that it is not too harsh. Probably 30-40 ppm CYA is plenty for that purpose. In hotter water there active chlorine level is higher at the same FC/CYA ratio compared to cooler water.

You shouldn't need to use MPS if you are using hypochlorite. Are you using lithium hypochlorite because you have it on hand already? It's very expensive compared to using bleach or other sources of chlorine.

 

[Dibbler]

Whilst I have had spas for about 6 years now, I am only just learning how to 'use it properly' Lithium seems to be supplied in Aus as the standard product for this purpose, (probably because it retails for so much)
I had not given thought to using liquid chlorine/Bleach, I'll get on that
Thanks

 

[Dibbler]

An Update:

Using 12.5% Bleach (Pool Chlorine) putting 50ml in 1800Litres according to PoolMath should give a FC of 4ppm, a test strip suggests this is approx. correct.
After 12 hours overnight check the FC is 0, so my best guess is the Ozone is on all the time. This spa will be impossible to keep FC in.

This is brand new water from a fill last Friday as the spa had to be drained and moved anyway last week.

I'll keep my investigations up.