100% Chlorine Demand - Help!

[bdwoods]

I've been enjoying the dichlor/bleach method for about a month now - without any problems - super clear water, no odors, etc...

However, I noticed that my chlorine is dissipating quite quickly - more than I thought it should - I'm having to add some at least once daily even if I don't use the tub. So, I decided to test my CD - to see what happens.

I shocked the tub on Sunday with non-chlorine oxidizer, and had a FC of 3 when I started the CD test.

So, last night, starting at 3, I upped the FC to 10. I then let the tub sit for 24 hours without use. Because everything is so clear and clean, I expected to still see 7 or so ppm this evening.

It was ZERO!!!

I just re-read Nitro's CD post, and it says that this is bad - that something is using up the chlorine.

I have one thought - unsure if it could contribute....

I have one of those "scum sponges" that floats on the water soaking up excess oils etc... Could this full of bacteria and be using up the FC? I'm using a skimmer bag before the water gets to the filter (I clean the bag 2X per week) and the filter is brand new (unwrapped on Sunday).

Any suggestions or ideas would be helpful. We usually bathe when clean (and usually with no swimsuits), and only for maybe 15 minutes daily - not excessive use.

Other levels - TA = 90, PH = 7.5 on the dot, CYA ~40, temp 102.

Thanks for any help.

[chem geek]

Even though you bathe clean, if two of you soak for 15 minutes, then that's a half person-hour of soaking each day and would require around 1-3/4 teaspoons of Dichlor or 2.5 fluid ounce of 6% bleach, though that's a rough estimate. So you might have gotten behind in the dosing or had some unusual chlorine demand. Try repeating the experiment shocking again. Hopefully, it will improve and if it does then it says you are getting rid of whatever has accumulated so can continue to shock (say, to 15 ppm FC) until the chlorine demand (CD) returns to a more normal level of around 25% drop and certainly less than 50%.

You could check your CYA reading if you are only assuming that it's 40 ppm. It's unlikely, but possible, for it to have dropped and if it did by a lot then the chlorine can outgas much more quickly.

When you add chlorine to the spa, after around 10 minutes or so of mixing with the circulation pump does the Free Chlorine (FC) still register or is it seen as Combined Chlorine (CC) instead?

[bdwoods]

When you add chlorine to the spa, after around 10 minutes or so of mixing with the circulation pump does the Free Chlorine (FC) still register or is it seen as Combined Chlorine (CC) instead?

Sorry, I'm not sure how to tell the difference. I know with my drop kit, if you leave it for 10 minutes, it reads the CC. Is this how you determine which is which between FC and CC?

[chem geek]

That's not a good way to tell. I thought you had the Taylor K-2006 or the TF100 from tftestkits.net since these have a FAS-DPD chlorine test that can measure accurately to within 0.2 ppm (or 0.5 ppm depending on sample size) for both Free Chlorine (FC) and Combined Chlorine (CC). A demo of the test can be seen here. If you already have a Taylor K-2005 or equivalent, you can get just the FAS-DPD chlorine test from tftestkits.net here.

[bdwoods]

That's not a good way to tell. I thought you had the Taylor K-2006 or the TF100 from tftestkits.net since these have a FAS-DPD chlorine test that can measure accurately to within 0.2 ppm (or 0.5 ppm depending on sample size) for both Free Chlorine (FC) and Combined Chlorine (CC). A demo of the test can be seen here. If you already have a Taylor K-2005 or equivalent, you can get just the FAS-DPD chlorine test from tftestkits.net here.

I don't have a taylor 2006 - they're a bit hard to find in Canada - without spending a couple hundred bucks.

I have a Taylor small kit - measures FC with pink dyes - does this mean its measuring CC? The label says it is measring FC. I need to get a 2006

[Nitro]

As Chem Geek said, try testing CD again to see if it drops.

Also, is your filter clean? A dirty filter can raise CD.

The best (only) way to lower CD is to shock. Add an ounce or two of MPS (non-chlorine shock), and a cup or two of bleach. Do this everyday until your CD is at or below 50%.

My quess is you got behind in your Chlorine additions. The good news is you caught it before it became a problem. Just try to add more in the future.