Here's Another Question

[rckymtntim]

Just returned from my vacation. Checking my FC levels and had an FC of 3.6, I guess I did pretty well before leaving. I have been using Nitro's dichlor bleach method. My CYA had been staying pretty steady at about 35ppm. On 1/17/2010 my CYA was 35ppm that was the last time I checked it. Here it is a month later and my CYA was down to 0. I did add about 9 gallons of water to the tub before checking and just changed my filters before testing. Does this seem right? I tested my CYA 2 times getting the same result both times. Could it be that the fresh water hadn't mixed yet, I did just add the water immediately before taking my test water.Do I need to back to adding dichlor to get my CYA level back up? My water is crystal clear.

Current readings with Taylor test kit:

FC= 3.6

PH= 7.7

TA= 60

CH= 170

CYA= 0

[chem geek]

That is very strange. The normal drop in CYA seen by most reports on this forum is around 5 ppm per month. The other way that CYA can drop quickly is if the chlorine level gets to zero and bacteria convert the 35 ppm CYA into 10.7 ppm ammonia, but then you would have a very large chlorine demand of at least 80 ppm FC cumulative so seems unlikely as you would have noticed that (unless all the ammonia were to outgas -- also unlikely).

I'd wait for the water to mix better and then retest. If it's still low, you can use Dichlor for a while to get it back up again.

[NewB@Spa]

I have a question related to that. If I plan to refill every 3 to 4 months do I even need to retest my CYA between fills?

[oldparr]

I have a question related to that. If I plan to refill every 3 to 4 months do I even need to retest my CYA between fills?

I used to do that (testing every month). Now after the first 30 ppm, I add 5ppm of CYA every month (using conditioner - isocyanuric acid 100%) and rarely test for it.

[NewB@Spa]

Wouldn't it be easier to just dose with Dichlor a couple of times (instead of bleach) to get CYA back up? I just hate to buy another chem just to use it once or twice.

[oldparr]

Wouldn't it be easier to just dose with Dichlor a couple of times (instead of bleach) to get CYA back up? I just hate to buy another chem just to use it once or twice.

I think it would be easier, but when I got my tub, I bought tons of stuff. One of them was 100% CYA. Now I have to use it. 100% CYA might be cheaper too, but I never did a good calculation on that.

[chem geek]

The pure CYA is about half the price (for the same CYA level) as the liquid CYA (Instant Pool Water Conditioner), but pure CYA takes a while to dissolve and is acidic.

[rckymtntim]

Here's a little more info on my issue. On 2/17 I had a FC reading of 3.6ppm and CYA 0ppm. I put in new filters. On 2/18 I checked and had FC of 2ppm so about a 45% chlorine demand. I added 1TBS dichlor to my 165 gal. spa. Retested and got a FC reading of 12ppm and CYA of 10ppm. Checked again today 2/19 FC=6.2ppm and demand at about 49%. Cya is up to about 25 ( just guessing as the water was above the 30ppm line on the Taylor test kit).

The CD seems high for having new filters and good test results. Is it time for a water change. The last change was 9/18/09. I was hoping to make it until the weather gets a bit warmer here in Colorado.

[chem geek]

Since your spa is small at 165 gallons, going 5+ months is quite a lot so yes, your water probably needs to be changed. In fact, if you are using the spa every day, then you probably need to change the water at around 3-4 months. That's still better than with Dichlor-only where you'd need to change it around twice as often and the water might be duller when doing so.

Since you have an ozonator, I wonder if it's really working since it should have gotten rid of more organics in the spa and not had the CD climb as much. The ozone itself would contribute to CD, but should be constant over time.