FC dropped to zero in spa

[GuinnessPhish]

Split by moderator from HERE. jblizzle

If FC were to fall to zero for about a day, what would be the best course of action?

Bring FC up to shock level for the CYA level? Drain and refill?

 

[chem geek]

Re: How do I use Chlorine in my Spa (or pool)?

For a whole day, you might need to do a decontamination which would require a drain/refill after the treatment (either Spa System Flush or superchlorination) in order to remove biofilms. Bacteria double in population in 15-60 minutes under ideal conditions so while well-established biofilms that are significantly resistant to chlorine might not be formed in a few hours, a whole day (24 hours) could be a problem. Even 8 hours could theoretically be a problem though in practice I think regular shock levels would be sufficient in that situation.

It's a statistical thing depending on nutrients and other conditions. I've seen reports of biofilm within a day or two. Not every time, though. I also assume you don't have an ozonator. Though it doesn't provide a consistent residual, there is usually a little ozone getting into the spa water so takes the edge off of growth, but not enough to completely prevent problems.

You could just see if you've got unusual chlorine demand that is higher than normal. That's the primary indicator for biofilms. Slimy surfaces would be another, but biofilms could be in your pipes or filter so chlorine demand is a more clear indicator, at least when there is a lot of biofilm.

 

[GuinnessPhish]

Re: How do I use Chlorine in my Spa (or pool)?

Just curious...

why couldn't the spa be put through the chlorine shock process just like a pool?

 

[GuinnessPhish]

Re: How do I use Chlorine in my Spa (or pool)?

Still waiting for an answer to the above question....


but I'll ask another anyway...


how often is it suggested to do a spa system flush? Do you only do it when you suspect biofilms, or should you do it once a year or so anyway?

 

[chem geek]

Re: How do I use Chlorine in my Spa (or pool)?

Because of the hotter temperatures and the much higher bather load, so more organics in the water, spas get much nastier when they go south. Whereas pools tend to develop green algae, spas tend to grow bacteria and form thick biofilms. Regular shock level isn't enough to get rid of established biofilms. Fortunately, they tend to rarely develop in residential pools even when the chlorine gets too low -- we've only had a handful of such reports of either biofilm or white water mold which can also be difficult once established.

As for the frequency of decontamination for spas, it's really only necessary once when you get started assuming you always subsequently have a disinfectant in your spa -- or at least don't let it go to zero for more than a few hours, certainly not 24.

 

[GuinnessPhish]

Re: How do I use Chlorine in my Spa (or pool)?

You could just see if you've got unusual chlorine demand that is higher than normal. That's the primary indicator for biofilms. Slimy surfaces would be another, but biofilms could be in your pipes or filter so chlorine demand is a more clear indicator, at least when there is a lot of biofilm.

So, my water is clear, and smells and feels fine, but I have been shocking it to about FC 14. In about 11 hours, my FC dropped 3.5, from FC 14 to FC 10.5.

I guess I should just go ahead and do a spa system flush.

 

[chem geek]

Re: How do I use Chlorine in my Spa (or pool)?

What is the water temp? If it's hot (100+), then a 25% FC loss in 24 hours is normal. If it's just warm (80ºF), then a 10-15% FC loss would be more common assuming there is no exposure to sunlight. Your loss is 1 - (10.5/14)^(24/11) = 47% so that does seem too high regardless. Also, do you have an ozonator? If so, then loss rates are about double in that situation so if your water is hot and you have an ozonator, then the loss rate you are seeing is probably normal.

 

[GuinnessPhish]

Re: How do I use Chlorine in my Spa (or pool)?

Water temp is about 95. The hot tub does have an ozonator, but I don't know how much or if it still works, as we bought the house last year, and don't know if the previous owner ever replaced the ozonator.

Went to the spa store, and they don't carry spa system flush (WTH?!).

Guess I'll test the FC level again at about 11pm tonight to see what I'm working with. I'll rinse my filter as well, as I haven't done that in quite a while.

 

[GuinnessPhish]

Re: How do I use Chlorine in my Spa (or pool)?

I tested at about 9:30....

shows FC 8

so, in almost 24 hours, I went from FC 14 to FC 8 with no real sunlight exposure, and temperatures between 91 and 95.

I'm going to shock to around FC 13, and then test again tomorrow night around 11pm...keeping the thermostat set only to 85, as we don't really use the hot tub too much during the week.

 

[chem geek]

Re: How do I use Chlorine in my Spa (or pool)?

Well with an ozonator what you are seeing may be fairly normal. An ozonator is helpful when the bather load is high since the ozone will oxidize some bather waste so that chlorine doesn't have to with the result that chlorine demand is lowered. However, if you don't soak every day or two, then the ozonator will create a higher chlorine demand because ozone reacts with chlorine.