Intellichem owners, need some experienced advice please

[Lershac]

Hi, new intellichem owner here.

I just installed my intellichem about a week ago, acid pump and intellichlor (IC40). Prior to installation, I shocked to be sure I had nothing going algae wise (pretty sure I didn't but I wanted a "clean slate"), and made sure I was balanced as far as the LSI etc. I have 40 ppm stabilizer.

What I am seeing a few days into this, is that the PH is rock stable, but the orp fluctuates with the sun. I am set at 700 on the ORP, and it goes up to ~750 overnight and stops the feed on the IC40, and then as SOON as the sun comes up around 6 (still hasnt hit the pool yet) it starts dropping steadily to around 580 to 630 and stabilizes there for the day. The sun actually hits the pool around 9 am and is on it full at this time of year until about 3 when it slowly moves off the pool over the course of a couple of hours until 7 when it is completely shaded.

Now during this time from 9-3 and on until 7 the ORP is pretty stable around 610, and when the sun actually goes down, starts to rise again. The IC40 is on steady from 6am until well past dark when it eventually climbs back up to around 750 in the wee hours and cuts off.


Thoughts?

I may be drawing a causational relationship that does not exist between the sun and the ORP reading here, but there is a definite time correlation between the sun rising and the ORP fluctuations.

This is also happening on overcast days. just another bit of data.

So I have a few questions/ideas...

1. Is this normal?
2. if the answer to #1 is NO, what can I do, get a bigger cell to keep up with the chlorine demand? I would think what I have would keep up, its rated for 2.5 times the pool size I have. Cost is not much of an issue, I dont mind getting a new bigger cell if its going to do the job. If the answer to #1 is YES,... whew! ok!
3. Why is it happening even before the sun actually hits the pool? I had the idea that UV was DIRECT sunlight and not the indirect stuff diffused by the atmosphere?

The pool looks AWESOME. And I am going to jamaica for a week or two and this really sets my mind at ease, between this and the poolskim, all my house-sitter has to do is empty the skimmers and the poolskim and drink beer!

 

[Lershac]

So after another week, things seem to have stabilized a bit more. I upped the target ORP to 760, and it oscillates around there as described above but, the low seems to be around 730 and the high seems to be around 820. All in all, very happy so far with it.

 

[JasonLion]

1) Yes, that is unfortunately quite common. ORP sensors are a fundamentally flawed concept, made much worse by pairing them with a SWG.
2) You aren't having a problem with keeping up with the chlorine demand, you are having a problem with the sensor returning nonsense results.
3) You get some UV in the very early morning, just not much. Still that is enough to have some effect.

One effect you are seeing, but haven't figured out yet, is that ORP will go down while the cell is on, even though the FC level is going up. This is caused by dissolved hydrogen gas, produced by the SWG cell. Hydrogen gas lower ORP. Then when the sun goes down it finally gets far enough ahead that the SWG turns off, hydrogen starts outgassing faster than it is being added, and ORP zooms up to a level more consistent with your FC level.

This is a large part of why I never recommend ORP based controllers for outdoor pools. If you switch to the simpler percentages based control of the SWG you will have more consistent FC levels and the cell will last far far longer than it will in the mode you are using right now.

 

[Lershac]

What still bothers me about it, is that the device reports an ORP OVER the target level, yet still has the SWG on. Total, its running about the percentage I had it set prior to purchasing the intellichem, but just at different times of the day. The measured FC level seems about right, but havent done anything like hourly measurements to try to match the reported ORP against the measured FC a every hour of the day.