Intellichem Owners - where to start with Chemistry on new pool

[dw886]

I'm just getting close to opening the pool for the first time - and along with that figuring out a starting point for water chemistry. It was installed / filled last fall, hooked up the autocover, and then we closed it up. The weather is getting warmer up north, so I'm trying to complete my plan for how I start. I've been doing reading - I thought I had everything figured out after going through Pool School multiple times and using Pool Math. Then I went back and started reading about others' experiences with similar equipment setups. Adam T's DIY Pool Automation document is nearly identical to what I have for equipment.

I know that the recommended range for CYA on a SWG pool is between 70-80, however I've also read that with the Intellichem, that if your CYA is over 20, then the ORP doesn't function correctly. Since CYA and FC are directly related, I know that I need to figure out where I want to start for CYA before I can really gauge what my FC should be.

So for those that use the Pentair Intellichem (with a SWG and automatic dosing of MA), what should I target for my CYA?

Our pool has an autocover, and will be covered 99% of the time (with the exceptions being weekday evenings when the kids want to swim, and weekend days when they're in the water). I'm anal about both safety and cleanliness, so it'll be closed if we're not by the pool.

 

[JoyfulNoise]

If the pool is closed, as you say, 99% of the time, then you should be able to use lower CYA and FC level. For an ORP based control system, you're going to need to limit the CYA or else the hypochlorous acid level will be too low and the signal-to-noise ratio will go way down (HOCl is the primary oxidant that changes the voltage at the probe, other chemicals and sunlight can affect the ORP voltage as well).

I would start of at the lowest possible level of CYA you can reliably measure which will be 30ppm. Then you can ask the ORP controller to try to hold your FC between 2-3ppm (whatever voltage that corresponds to). Given the pool will have low bather load and no UV loss, the ORP controller should be able to function properly. Your best bet is to measure your FC very regularly so you can correlate the FC in the water with the ORP set point voltage. Once you feel like you can get a good correlation, you can then switch over to spot testing a few times per week. Be sure to regularly clean and calibrate your ORP probe as CYA tends to foul the glass membrane on them. Regular inspection of the probes (once per month at a minimum, in my opinion) is necessary to ensure they are working correctly.

The pH controller should do fine, those are rarely problematic except for probe failure. Keep regular tabs on your pH and TA to ensure that your water quality remains in the comfortable range for swimming. You can keep your TA a little on the higher side because there will be very little outgassing of CO2 with the cover on. The outgassing of CO2 from the water is the primary reason why pH rises. If the pool were open more, then you'd need to lower TA. But a covered pool should be fine to operate the TA between 80-100ppm. pH can be anywhere between 7.2-7.8 for bather comfort but, to keep acid demand low, I'd just shoot for 7.6-7.7 and let the pool ride there.

 

[dw886]

Thanks Matt - very informative. I need to pull some preliminary numbers with my test kit (both for practice and to see what my water composition actually is) - I'm assuming that I'm at 0 for CYA and chlorine but it'll be good practice to test and validate. I'll shoot for CYA of 30. What's interesting is another swing through the IntelliChem book for install over the weekend I noticed that it tells you CYA of 30-50 as "ideal".