When To Drain/refill?

[spidey9]

I have a Jacuzzi J-345 (340 gal) that I purchased last summer. I switched from Silk Balance to the Dichlor/Bleach method the first time I refilled it. We use the tub daily for a 20 min session with one or two people, and I add 2-4 oz of bleach each night after we're done. I check pH and Cl daily, and do a full set of tests (Taylor K2006) weekly. Here are my most recent numbers:

pH: 7.6

FC: 3.2

CC: 0.4

TA: 70

CH: 150

CYA: 34

It has now been nearly 4 months since the water change. Water is crystal clear, and odorless except for a slight whiff of chlorine when I first open the cover.

I also have a SafeDip pool & spa tester that measures Salt and Total Dissolved Solids (TDS). After the initial balancing (and adding 50 ppm borates) when I did the refill I got:

Salt: 300 ppm

TDS: 500 ppm

We also frequently add Cover Valet Aromatherapy Spa Crystals, which according to the label contain epsom salts and sea salt.

Current readings:

Salt:2000 ppm

TDS: 3200 ppm

So, is it time to change the water?:

[BinaryBob]

Those are amazing numbers after 4 months of nearly daily use. Do you sterilize yourselves berfore entering the spa? :-)

I'd look at the pinned article "chlorine demand". Excessive demand is when I determine it's water change time.

[chem geek]

Chlorine demand is a good way to tell. Without an ozonator, after a fresh refill it's usually a 24-hour loss rate (with no bather load) of 25% or so while after extensive use over time this creeps up to around 50% at which point you can change the water. The standard Water Replacement Interval (WRI) formula is (1/3) x (Spa Size in Gallons) / (# of bathers) where I presume they assume 20 minute soaks, but with Dichlor-then-bleach one should be able to go at least twice as long so in person-hours this is (2/9) x (Spa Size in Gallons) / (# of person-hours per day) so this is (2/9) x 340 / (1.5 x 20/60) = 151 days or around 5 months. So it sounds like you are on the right track and the Dichlor-then-bleach method is working well for you.

Don't forget to add some Dichlor, probably around once a month for a day, to keep the CYA up at roughly 40 ppm. The CYA will slowly get oxidized by chlorine over time.

As for the TDS, 2.5 fluid ounces of 6% bleach every day would increase salt and TDS by around 5.9 per day or 178 per month so around 700 or so after 4 months. You've had around 1700 ppm which is higher than I would have expected. Maybe your tester isn't accurate. I doubt that the TDS level is that much higher than the salt level for a conductivity meter since most of the TDS is salt (unless your CH was high). The borates don't measure much as TDS since they are mostly boric acid that is neutral. The risk at high salt or TDS levels is increased metal corrosion rates. If you really want to know the salt accurately, there is the http://www.taylortechnologies.com/products_kitinfo.asp?&MarketID=1&KitID=2176'>Taylor K-1766.

[spidey9]

Thanks for the responses. The tub does not have an ozonator, but does have the ClearRay UV system - I don't know what effect that has on anything.

I know that I need to test for chlorine demand, but I keep putting it off because I don't want to go 24 hours without using the tub.

I've actually been adding about a teaspoon of CYA once a month.

I have no way of knowing how accurate the SafeDip tester is, although it also measures pH and that is usually in line with the Taylor test. Thanks for the tip on the K-1766 kit - I may order one just to check the accuracy of the tester.

All that being said, I'm leaning toward changing the water this weekend.

Which brings up another question: I have ordered some SeaKlear Spa System Flush. Is it a good idea to use this every time I change the water?

[chem geek]

If the spa is properly maintained, then you normally would not need to use Spa System Flush on every water change. That said, some people have reported seeing gunk come out when using Spa System Flush even after maintaining with chlorine properly. I'd say, why don't you use it this time by adding it before you drain (as directed) and let us know what you find out. This is one of those things where we won't be able to give a decent recommendation without more real-life examples.

[spidey9]

Per the Spa System Flush directions, after my soak last night I pulled the filters, added 7 oz of Spa System Flush and ran the pumps through a couple of cycles. Afterwards I noted that the water was slightly cloudy and smelled funky, but was otherwise okay - no gunk floating around. I let it drain overnight.

Today I cleaned, refilled, and balanced the water. After adding dry acid and aerating a couple of times, I got to pH 7.4 and TA 70 (initially 8.0/100 respectively). As has been reported here, when I added 9 oz Pro Team Gentle Spa, pH spiked to 8+. Using the Taylor acid demand test, I added 1.25 oz of dry acid to bring it back in line.

Another 10 degrees and I'll be back in business.