Interesting Finding On Chlorine Demand And Filters....

[bart6453]

So I keep a log of my chlorine demand every week just to keep an eye on it to make sure that my tub is not infected.

I noticed since the last fill that my CD continued a very consistent climb from 20% to nearly 50% over a 90 day period. I shock my tub regularly with MPS when my CC climbs close to 1ppm.

After doing a filter change (I know I should do it more often, but I was testing my hypothesis) at the 90 day mark, my CD went from nearly 50% to 20% in 1 day.

My hypothesis was that the filters trapped organic matter and of course it builds up over time. The very structure of the filter makes it difficult for the chlorine to oxidize the organics that are built up on them. This in turn contributes to excessive CD.

Very interesting that a clean set of filters can take my CD down 30%.

I will continue to log my CD and my filter changes to see if this continues to hold true.

I guess what I am getting at is that cleanliness is next to godliness in the hot tub filter world.

[chem geek]

Sounds very reasonable. I don't think the filters necessarily make it more difficult for chlorine to oxidize what is in them, but rather that there is a range of substances introduced into the spa and some of them are rather slow to oxidize. These build up in the filter so increase chlorine demand. So yes, cleaning/changing the filter makes a difference and is something that should be done as part of spa maintenance.

I wonder if these extra substances are things like dead skin or whether it's oils/lotions on the skin. That is, I wonder if the buildup would occur as quickly if one were clean (i.e. showered) when using the tub. Normal sweat and urine should mostly get oxidized fairly quickly.

Another option one can try is the use of an enzyme product as that should help break down these slower-to-oxidize chemicals, depending on the quality of the enzyme. It's just another option to consider. There's nothing wrong with regular cleaning/changing of filters except for the inconvenience/expense.

[bart6453]

Sounds very reasonable. I don't think the filters necessarily make it more difficult for chlorine to oxidize what is in them, but rather that there is a range of substances introduced into the spa and some of them are rather slow to oxidize. These build up in the filter so increase chlorine demand. So yes, cleaning/changing the filter makes a difference and is something that should be done as part of spa maintenance.

I wonder if these extra substances are things like dead skin or whether it's oils/lotions on the skin. That is, I wonder if the buildup would occur as quickly if one were clean (i.e. showered) when using the tub. Normal sweat and urine should mostly get oxidized fairly quickly.

Another option one can try is the use of an enzyme product as that should help break down these slower-to-oxidize chemicals, depending on the quality of the enzyme. It's just another option to consider. There's nothing wrong with regular cleaning/changing of filters except for the inconvenience/expense.

That would be an interesting test to wash regularly before getting in the tub.

I can say that as part of this test we did, for the past 90 days it has only been my wife and I in the tub. We rinsed our hair of products and removed underarm prior to EVERY soak. Also at no time were any fabrics introduced into the tub.

I am very reasonably sure that the contents of the filter were simply body oils and stray hair. I inspected the filter pleats and found much more hair than I thought I would. There was also a fine grime layer that I am reasonably sure is dead skin and body oils.

In short, the filter's performance truly impressed me. By virtue of them catching all the crud they do a very good job.

Now the question is to how often to clean? should one clean the filters more regularly, or as with shocking...should one clean the filters as indicated by water maintenance instead of the day of the month?

I have two sets of filters, so it really is not a problem for me to change them more frequently. Just more of an educational thing for me.

[chem geek]

Since the amount and quality of bather load is going to affect the chlorine demand, I would say that you should clean your filters based more on when the chlorine demand starts to climb significantly. This is somewhat analogous to pools when you clean the filter when the pressure rises above a certain amount, which indicates that the filter has caught a lot of material. Since the chlorine demand could still be OK but there could be items caught in the filter that don't use up chlorine, there should probably also be a maximum time when the filter should be cleaned/replaced. As for specifics on when this should all be, I defer to those with experience in this area for what is reasonable and works best.

I suspect that the hair was the primary source of chlorine demand since it is mostly composed of keratin which are proteins which are made up of amino acids, all of which have an ammonia-like group (except for proline that has a nitrogen in a non-aromatic ring). It's a large surface area to react with, but the keratin strands are tightly bound by disulfide bonds (from the cysteine amino acid) so it takes chlorine a while to break it down. That means the hair builds up over time but uses up some chlorine so with more hair their is more chlorine consumption. It's possible the dead skin and body oils are a factor, though I suspect in that case that the chlorine has more readily reacted where it can with these and that they are simply not fully oxidized but do not react as much with chlorine. Of course, one could do an experiment with these two parts separately to see what is really true. Though that might be considered an academic exercise, if it turns out that hair is the primary source of chlorine demand, then using a hair net or hair tie might help (if someone really cares that much about this and wants to avoid cleaning their filter as often).

[bart6453]

Since the amount and quality of bather load is going to affect the chlorine demand, I would say that you should clean your filters based more on when the chlorine demand starts to climb significantly. This is somewhat analogous to pools when you clean the filter when the pressure rises above a certain amount, which indicates that the filter has caught a lot of material. Since the chlorine demand could still be OK but there could be items caught in the filter that don't use up chlorine, there should probably also be a maximum time when the filter should be cleaned/replaced. As for specifics on when this should all be, I defer to those with experience in this area for what is reasonable and works best.

I suspect that the hair was the primary source of chlorine demand since it is mostly composed of keratin which are proteins which are made up of amino acids, all of which have an ammonia-like group (except for proline that has a nitrogen in a non-aromatic ring). It's a large surface area to react with, but the keratin strands are tightly bound by disulfide bonds (from the cysteine amino acid) so it takes chlorine a while to break it down. That means the hair builds up over time but uses up some chlorine so with more hair their is more chlorine consumption. It's possible the dead skin and body oils are a factor, though I suspect in that case that the chlorine has more readily reacted where it can with these and that they are simply not fully oxidized but do not react as much with chlorine. Of course, one could do an experiment with these two parts separately to see what is really true. Though that might be considered an academic exercise, if it turns out that hair is the primary source of chlorine demand, then using a hair net or hair tie might help (if someone really cares that much about this and wants to avoid cleaning their filter as often).

I agree academic at best.....but interesting.

on a hair net...I would have to wrap myself in cheese cloth...I am a furry fat beast.

I agree on the max time frame with CD consideration. I believe I will be on a 90 day max cycle while keeping an eye on CD if it goes over 45% I will clean the filters.

Kind of an fun study...though.

[pondlife]

Wanted

bald husband and wife team for chlorine demand research project.

[bart6453]

Wanted

bald husband and wife team for chlorine demand research project.

You should post that on an Alopecia board....might get a better response....ok...I am horrible...sorry God.