Extremely High Bather Load

[jakenz]

Hi Everyone,

Great forum, i have learnt a lot over the last week reading and rereading how to maintain a spa.

I am a university student flatting with another 3 guys, just recently we decided to get a spa, and have purchased a 1050l (275 gallon) tub.

After a few, well more than a few false starts, especially with using dichlor and the cya very quickly getting out of control i have decided to start using the dichlor then bleach method.

The first issue im having is getting a decent water testing kit, the Taylor K2006 seems to be what is recommended, however it is not available in New Zealand, does anyone know of an alternative, or a way for me to get a taylor over here.

The biggest issue im facing is bather load, being at university having a spa has attracted many other students over for parties, in which alot of drink is consumed and probably spilled in the spa. One night we had an average of 6 people in the spa for about 6 hours, all getting in and out constantly.

I worked this out using the 7ppm per person per hour method, i understand that this is for a 350 gallon tub so in reality its probably more, anyhow this comes to a whopping 252ppm of FC needed after the party!

To be honest i dont know what to do here, this seems like a far to greater amount of chlorine to be adding at once, i understand that some of this will be needed to be added during the night to maintain some level of FC, but it will still be a huge dose at the end of the night.

If someone could advise me on how to cope with ths situation it would be very much appreciated.

Thanks in advance

[chem geek]

I suspect that the spa wasn't staying at a hot 104ºF (40ºC) so the average of 6 people in the tub at any given time probably weren't sweating as much as a result. Also, did you seriously get 6 people in the tub the entire 6 hours with only 275 gallons? That also seems unlikely and all 6 probably weren't completely immersed (to their shoulders) either.

If you don't have an ozonator, then it would probably take a lot of chlorine to oxidize all the bather waste from such a large event. If you have an ozonator, then it will likely handle at least half of the bather load if not more.

Anyway, you could just add much lower amounts of chlorine, around 20 ppm FC at a time, and measure the FC level an hour or so later. If it mostly measures as CC or the FC gets mostly used up, then add more chlorine.

Without a proper test kit, it will be tough. This is one situation where a FAS-DPD chlorine test kit is very useful since it won't bleach out at high FC (you at least get a flash of pink and can add more DPD powder) and you can properly distinguish between FC and CC. See if you can get the Palintest FAS-DPD SP 300 test kit.

Of course, you always have the option of just dumping the water and starting over.

[jakenz]

Thanks chem geek,

As for the amount of people in the spa, we got in at about 5pm with 7 of us in it and everyone was out of the spa by 12, the amount of people dwindled a bit towards the end of the night, but there were probably about 12-15 different people using it in total, but this has been our biggest night so far and with the amount of cya in at that stage required the spa to be drained as it was still cloudy 3 days later with a FC ppm of over 10 constantly.

Also the spa has been used the past 2 nights with the new fill, 1st night with 4 people for 2 hours, and the 2nd 2 for an hour and a half, after the first night i added 56ppm of FC to find that by the time we came to use the spa tonight it was still over 10ppm, and after an hour still over 10ppm, (according to the test strips we have) so i feel maybe 56ppm was too much?

The spa is mostly used for watching movies, so is set for 38c and gets turned off during and dips to about 34-35 by the end, so in that regard maybe the bather load is lightened.

I like the idea of adding 20ppm at a time after high use, do i keep doing this until i have added the required amount of ppm for the load, or until the FC stabilises?

I did a search for the sp 300 and found nothing, but it looks like there is a stockist in nz for palintest products so i will get in touch with them and see if they can get one in.

My apologies if my message is a little hard to read, St Patricks day today..

Thanks again

[chem geek]

Does your spa have an ozonator? I don't think you ever answered that question.

When adding 20 ppm FC at a time after a heavy bather load, you keep adding it if the FC level drops substantially (say to 5 ppm or below) after an hour or so. When the FC is dropping that fast, it means there is a lot to oxidize.

As for your 56 ppm example, yes that was too much since the chlorine didn't drop down to reasonable levels closer to 2 ppm that you'd probably appreciate at the start of your soak. You'll just have to tweak until you figure your person-hour chlorine amount for your spa given your cleanliness, amount you dip into the water, water temperature, etc. That is, you experimentally determine this, but the good news is that it won't change very much, at least for consistent usage (i.e. same people using the spa in the same way).

Now as for what to do regarding disinfection during your soak, that's a tough one. For most people who soak for no more than 1 hour (many are just 20-30 minutes), there shouldn't be any problem starting out with 2 ppm FC at the start of their soak in which case most of this will get converted to monochloramine during their soak (due to the ammonia in sweat and urine) and will provide some lesser level of slower disinfection during their soak. Also, bacteria won't reproduce very much in just one hour -- they might increase 16x in population best case (but given the monochloramine, that's unlikely). Then when people dose with chlorine after the soak, they kill off whatever is remaining and oxidize their bather waste.

However, in your case, you are soaking for much more an hour and sometimes for 7 hours. One bacterium can turn into over one-quarter billion in 7 hours under ideal conditions. Yes, there will be some monochloramine, at least initially, but it would probably be better to continue to dose with some chlorine every hour, say 2 ppm at least. Obviously you have to be very careful doing that with people in the spa -- pre-dilute the chlorine and slowly pour it in, perhaps into the skimmer or equivalent that would go into the circulation system.

[jakenz]

No our spa does not have an ozonator, we thought about getting one, but do not have the money for it at this stage.

Thanks for the advise, i think that finding the right dosage after bathing will be the next thing i have to get sorted.

We have found no issues with using the spa even with high FC levels of around 10ppm, so maybe before a party just get the FC fairly high then redose halfway though, with a couple minutes out of the sps to let it mix.

I added borates to the spa yesterday, so hopefully that will help with keeping the ph steady, have been finding that the ph rise has been difficult to keep on top of due to 2 of the jets having air constantly coming through them regardless of the setting.

[chem geek]

The main issue with the higher FC (assuming you have CYA in the water to moderate chlorine's strength) is that you will likely smell it, especially after it reacts with your sweat to form monochloramine. Some people don't like that so they start their soak with 1-2 ppm FC so they don't notice the smell (or it's very faint). It's really up to you. You will get more disinfection with the higher FC level. 10 ppm without CYA would be way, way too much, but with 30-40 ppm CYA in the water then even at hot spa temperatures it's equivalent to 1.65 ppm FC with non CYA. That's on the high side and you'd probably not want to do that every day unless you don't care about your swimsuits degrading more quickly. 5 ppm FC might be a more reasonable balance, but it's really up to you. Technically, the EPA sets a limit for spas of 5 ppm, but various state codes for pools go up to 10 ppm (Florida, for example) at least in part because the outdoor pools usually have CYA in them.

Keep us posted on the pH since the borates should help slow down the rate of rise, though shouldn't change the amount of acid you need to add per time (though since you'll be adding it less frequently, you'll add a larger quantity when you do add it and it takes more acid to move the pH back down when borates are present).

[jakenz]

Yeah i think ill aim for 5ppm, spa should currently have around 30ppm cya, water test from the local spa shop says 60, but im doubting the accuracy of that,

Going by the pool calculator, with my current TA of 50, i need a really high CH to compensate for that, in the region on 400ppm, i have taken the spa to 160ppm with calcium chloride, do i need to take this higher, or it it ok to just use calcium hypo as our source of FC and not worry about it?

[chem geek]

I wouldn't go too high with the CH since you want to avoid calcium carbonate scaling, especially in the heater. If you plan to use Cal-Hypo, you should start with a lower CH since for every 10 ppm FC added by Cal-Hypo it also increases CH by at least 7 ppm.

[jakenz]

What would you recommend as the CH level to aim for?

[jakenz]

Another pool test today, TA 25ppm, PH 8. Kinda lost as to what to do now

[chem geek]

A CH of 120-150 ppm is usually enough to prevent foaming and it's low enough that you don't need to worry about scaling (with a low TA) even if the pH rises. So how are you doing your testing? Since you don't have (and cannot get) a Taylor K-2006, I wonder if some of your tests are invalid. Also note that some borate products are not boric acid and may have the pH rise, so go ahead and add acid to lower the pH. I don't understand, however, how your TA got down to 25 ppm if you stopped adding acid when it hit around 50 ppm. You might need to raise it, but first see what happens if you get the pH down to 7.5 now that you've got borates in the water. If the borates are truly there, you'll find that you need to add more acid to get the pH lower than before you added the borates. That would be good news since it would be slower to rise back up in pH which is what it is supposed to do -- buffer the pH.

[jakenz]

I have been using the local pool and spa shops to get testing done, have noticed a few wild readings that i ignore, but mostly seem to be ok. I used alot of ph down to counter the rise from adding borax, but even after i got it back down it continued to rise, ta is around 40 now, and judging by the test strips, not very reliable i know, but the pH seems to not be getting too high. I think the CH is around 200 now, and have changed to liquid chlorine, cant get good bleach around here.

[jakenz]

Im stuck again and not sure what to do, most of my numbers are ok now, apart from FC, the usage is crazy. The CD had been high so i have been shocking 20ppm for about a week now, this is taking additions of 200ml of 10% twice daily and i test twice daily and by the evening and again in the morning its down to 2ppm again, last night i shocked to 50ppm as was suggested on one post and its down to 10ppm already ~20 hours later.

The filters are about a month old and get rinsed twice a week. The water in the spa is crystal clear, ive never seen spa water so clear. And yet our CD is through the roof, what do i do?

[chem geek]

Did you use enough Dichlor to start with? It sounds like maybe your CYA level is too low so chlorine is outgassing or reacting too quickly. Also, if you keep a high shock level at high spa temperatures, it may break down CYA more quickly, though normal CYA breakdown in a spa is on the order of 5 ppm per month so it shouldn't be down that much in a short period of time. It's really too bad you can't get a proper test in New Zealand. That would help figure things out.

There's also the possibility that the chlorine isn't as strong as you think it is. Again, that's where an accurate FAS-DPD chlorine test would really help out.

[jakenz]

I had the water tested and the cya came back at 40, usually comes back between 35 and 60.

I thought i might have been getting somewhere, there was a 4ppm residual this morning, however i opened the cover tonight and it smelled rank and the fc was down to 0 again, dumped in the rest of our dichlor, maybe 15g and will have another look tomorrow morning.

I checked the strength of the chlorine, its around 9% judging by how much it raises the FC in the spa.

Is our spa just a dud?

[chem geek]

Well the extremely high bather loads probably called for a water change to be done at some point since chlorine doesn't oxidize everything, but if the zero chlorine levels were for too long and biofilms took hold then you'll probably need to decontaminate. I don't know if you've got SeaKlear Spa System Flush or can get AquaFinesse Spa Clean Tablet.