A Little Help With Sudden High Chlorine Demand

[lpad]

Pertinent information: Dimension 1 Nautilus (so has an ozone generator)

method: dichlor then bleach

last fresh fill: 10/2011

use: light, maybe 6-8 times this season, 2-3 people (either 2 adults or 1 adult plus two children who have showered before getting in)

water clarity: still looks clear to my eye

Chemistry:

Borates- 50ppm

pH- 7.9 (I've been struggling to keep it down despite lots of dry acid addition periodically)

TA- 70

Problem:

failing to keep up with the bleach addition faithfully, sometimes going a week in between additions if we haven't used it. Getting back into trying to be more diligent I started testing the water more routinely, first a quick check of Chlorine with strips....I noticed that even though I had added 8oz bleach the night before that the next day the strip indicated almost no Chlorine left, and the FAS/Dpd test confirmed, there was about 0.5-1 ppm Chlorine overnight after no use. So I knew we had a problem. Tried adding a cup of bleach again and next day same thing. So today I also added 10ppm of dichlor. I usually add 5ppm once a month because I read the CYA does fall off slowly each month. So I had added my regularly scheduled Dichlor on 1/1/2012, so this 10ppm dose I added today was just a bit earlier than my schedule.

Question: What else can I do at this point? Do I need to get some MPS? Because of the weather I would like to avoid running a decontamination procedure if at all possible, at least until the weather warms to the 40's.

[JimKW]

I am not an expert at all, but how are your filters? When mine starts using chlorine I just change the water and clean or replace the filters, which is about every three months, four at the most. But I have never used chlorine any where near the rate you are using it. Wish I could be more help.

[waterbear]

My suggestion, if you are not going to be giving the spa daily attention, would be to switch to 3 step bromine.

[lpad]

Additional info:

Jim: Filters were changed at the new water fill in October. We have two sets, so one set was clean and ready to go for October (we clean them by soaking in Cascade detergent with the phosphates in it)

Waterbear: Our intention is to get back on track with the dichlor then bleach method.

More Chlorine level info:

1/24 8:30am- added approximately 20ppm sanitizer, I did not measure with the Fas/dpd test at this point.

1/24 1:30pm- FAS/dpp-16ppm

1/24 5:45pm- FAS/dpd-15ppm

1/25 7:00am- FAS/dpd-8.5ppm

Do I keep adding high levels of bleach at this point?

Will an MPS shock help at all (I've never used MPS) so I don't know anything about how that works or how much I would use.

Would appreciate additional input on whether my tub is safe to use or how to get the CD lower.

Thank you

[waterbear]

Shock the tub with 50 ppm chlorine and keep the cover off and the circulation running until the chlorne level drops below 10 ppm. That should kill anything that is consuming your FC. Your CC should be 0 after this.

Also, please post full test results. It is helpful. Do you have any CC?

[lpad]

I tested CC. When I added the 5 drops of Reagent 3, the solution turned a very very pale pink, so there is at least some. One drop of titrating reagent cleared it up, so the CC is at 0.5ppm or possibly less.

I will do as you say, adding the 50ppm bleach. Thank you.

Edited to add: I did another FAS/DPD test at 1:30p and the Chlorine only dropped 1 ppm since I tested it 6.5 hours ago. It was at 7.5ppm and I brought it up to 50ppm with the bleach. At some point tonight I think I should close the spa lid (for safety and liability). Will that harm anything to have the lid closed with the high chlorine levels?

[lpad]

Another update :

After shocking to 50ppm yesterday I measured the chlorine levels this morning and it was all the way down to 20ppm. Is this bad? I will continue to measure the chlorine levels today. Any other input?