Dichlor dose isn't holding FC as long any more

[Chad]

Why Not,

The formula for when to change your water from the taylor book is

# of days = 1/3 volume (gal) by the Max # of daily bathers  

example from the book follows as:

1,200 gallon spa commerical spa is is used over the weekend by 200 people then you should change the water at 2 days
  
I have the taylor test kit k-2005 and it is on page 39

Hope this helps
CapMorgan

Thanks Cap Morgan. I found it. I must have thumbed right over it. It's the same as the one I just posted. I guess it must be the standard formula then for changing hot tub water.
Do you measure for TDS or can you just tell when it's time?

[CapMorgan]

Yes i do measure for TDS, i think they work ok i got my from DOC site.

CapMorgan

[Chad]

Yes i do measure for TDS, i think they work ok i got my from DOC site.

CapMorgan

Thanks again CapMorgan. I'll place an order.

[anne]

A couple more thoughts for you:  If I remember correctly, chlorine is 50% hypochlorous acid at pH 7.5 and 75% at 7.0, (roughly 5%/pt of pH) so the pH rise could account for 15% decrease in sanitizer efficiency.  

Reese, I was sort of thinking the same thing; certainly an increase in pH will render the chlorine present less effective, but he said that the measured FC was lower than expected......that doesn't make sense, does it? a pH increase, within reason, should not change the FC level on a taylor test kit, I dont think.....?

[Chad]

he said that the measured FC was lower than expected

Yes that it is correct. It's taking more dichlor to get the same FC reading lately.
For instance I added 1 TBS yesterday at 2:00 a.m. and 20 minutes later I had a FC of 6. Last month it would have been more like 8-10. Also, today at 7:00 a.m.(29 hrs. later) I tested for FC and none was present. Last month I was having some present 48 hrs later with that same post soak ppm. :-?

[Chad]

Thanks for all the help guys/girls. CapMorgan's links helped me find the culprit to my dichlor problems. I'm pretty sure it's just due to my high CYA level.

[Tyheethan]

So Why Not--how did this whole thing turn out?    Also, as a newbie, I don't know what CYA level is?  I think TDS is Total Dissolved Solids but not sure.  Also,  if you had high CYA or TDS, how would you/did you treat it?

Thanks!

Tyhee

[Chad]

So Why Not--how did this whole thing turn out?    Also, as a newbie, I don't know what CYA level is?  I think TDS is Total Dissolved Solids but not sure.  Also,  if you had high CYA or TDS, how would you/did you treat it?

Thanks!

Tyhee

Thanks for asking.  I've decided not to dump yet as I'm waiting for my TDS strips to arrive. That will be the deciding factor. I didn't want to dump just b/c my dichlor demand increased due to the high CYA. Afterall my water still clears up really fast after I turn the jets off and it still feels great.
Here is a link about CYA http://www.whatsthebest-hottub.com/cgi-bin/yabb/YaBB.pl?num=1167434259/30#30 Tony and Capmorgan helped me alot.
To answer your question about treating high CYA or TDS, the only way is to do a full or partial water change. Once they're present, they're there to stay.