Help with sizing Autopilot Digital SWG

[beezar]

I have a 18000 gallon pool and thinking about getting a Autopilot Digital.

I live in Texas, and haven't hit the hot summers yet, but currently losing about 2-3ppm chlorine a day (undoubtedly will go up with our very hot summers). I was trying to decide between the 35K rated SWG or the 42K rated SWG... I know bigger would mean longer cell life, but is there a disadvantage with going with the 42K SWG other than cost?

Thanks!

 

[Bama Rambler]

Until you get about 3x the size of the pool with the cell size you won't have a problem. The problem with getting a cell more than 3 times the pool size is that you have to run them at such a low percentage that it's not practical.

 

[JoshU]

Just like Dave said the 42k will work very well with your pool.

Any other questions for us?

 

[Poolsean]

2-3 ppm of chlorine loss is a little excessive. What Cyanuric acid level are you maintaining?
While you're at it, what's the rest of your water chemistry test results?

pH
Total Alkalinity
Calcium Hardness
CYA
Free Chlorine
Total Chlorine

 

[racket]

2-3 ppm of chlorine loss is a little excessive. What Cyanuric acid level are you maintaining?
While you're at it, what's the rest of your water chemistry test results?

pH
Total Alkalinity
Calcium Hardness
CYA
Free Chlorine
Total Chlorine

4,500 gallon spa, maybe this is a party pad??

 

[PoolDad2]

I don't mean to thread jack but I have been searching and not wanting to start a thread that has been covered. I just had a new liner installed in our 24k IG which is 18'x36' that has a Quad 60 DE filter. I was looking to find out what size SWG cell to get. Would the AquaRite 40k be to big? The pool store here wants to sell me a 25k.

I'm looking at installing a Goldline AquaRite SWG system. From what I have read they are well worth it and I found the Control panel and 40K cell for $1,050 so far.

 

[Bama Rambler]

PoolDad2, I'll answer your question here but it would be fine to start a new thread.

If your pool is 24,000 gallons then a cell rated for 25,000 gallons is too small. I wouldn't even consider the 25k unit. I'd go for the 40k or even bigger.

 

[PoolDad2]

Thanks for the reply. It pretty much answered my question. I spent some serious time going over all the threads and have found many answers that I had questions on.

This site is great!

 

[beezar]

2-3 ppm of chlorine loss is a little excessive. What Cyanuric acid level are you maintaining?
While you're at it, what's the rest of your water chemistry test results?

pH
Total Alkalinity
Calcium Hardness
CYA
Free Chlorine
Total Chlorine

Well, the CYA I'm "maintaining" is more like a CYA I am slowly trying to lower:

CYA 140
Free chlorine 15
Total chlorine 15
TA 90
pH 7.6
CH 290

The pool often gets lots of sun and it is starting to get a bit hot here in Texas...

 

[JasonLion]

With CYA that high and a loss of 2-3 ppm of FC per day you almost certainly have a low level algae problem. At high CYA levels it is very easy for there to be enough algae to use up lots of chlorine but not enough to be visible. It is very difficult to completely kill algae when CYA is that high.

 

[beezar]

With CYA that high and a loss of 2-3 ppm of FC per day you almost certainly have a low level algae problem. At high CYA levels it is very easy for there to be enough algae to use up lots of chlorine but not enough to be visible. It is very difficult to completely kill algae when CYA is that high.

Can you still have an algae problem if your CC is 0? Guess I'll have to do an overnight FC loss test to make sure. Thanks for making me aware of this! I just thought it was normal.... What kind of FC loss per day would you expect if there was no algae?

 

[JasonLion]

Sure, CC can easily be zero even when you have active and visible algae.

If there wasn't any algae, and with CYA at 140, I would expect daily chlorine usage to be below 0.5 ppm per day, possibly well below depending on how much direct sunlight you get on the pool.