How to Create CC

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investindy

investindy

0
Oct 21, 2008
51
Terre Haute, IN
Doing an experiment with an ORP sensor and want to take 5 gallon of water to O FC, create chloramines (CC?), and then use bleach to make my desired FC levels. I am going to use these values to create thresholds for my bleach dispensing system. I have testkits to make sure the water is a known value.....How can I easily create containaments in my bucket to simulate realworld to setup my ORP??? I dont care if my ORP is really at say 300mv and a calibrated one is 250MV at "x" FC level....I only care enough to dial in a known value based on my test kit and see the corresponding ORP value so I can dial in when to dispense bleach...I am working on the details for timing how much, when to retest, add more, etc.....
 
If you are calibrating an ORP sensor, I wouldn't bother with the CC or contaminant aspect. Just start with some pool water (something already adjusted for Calcium Hardness, Total Alkalinity, pH and Cyanuric Acid) and then add dropper amounts of bleach with different measurable FC and correlate that with the ORP reading. Of course, you'll have to redo that in a real pool since there is some variation based on a number of factors you can't exactly simulate in a bucket, but this will give you a rough idea. Basically, your thresholds should be based on the FC at a given pH and CYA. It has nothing to do with anything else. Any CCs will be taken care of by extra FC so it's FC that you need to focus on. Use the standard FC/CYA charts on this forum to figure out appropriate targets.

Richard
 
Understand.....Would the readings be somewhat linear from the ORP sensor? If my pool water is already at the FC level I need for my PH and CYA can I add the drops you get to neutralize Chlorine in Fish tanks to bring my FC level down so I can simulate low FC levels and the corresponding ORP reading?
 
Thought of that, was just trying to be able to dial it in where I wanted....I could keep going back and testing/waiting for my desired low FC level...I'm in the midwest with very little sun now and 40 degree nights with a high CYA level...Do not know what I'm getting into for the wait times. Or even if the water might get to freezing point before I get to my desired low FC level...Building my system for next spring. Guess I can just test with the fish drops and see if it works....Sensor is being shipped as I write this, so I'll post the results if the Neuralization drops work for FC....
 
3 follow-up questions for this thread....

Out of curiosity do you know if I will find at a constant PH that the ORP readings are linear based on the FC level (assuming all other things constant)? I can try and tweak things such that if my PH moves I am still covered when I need to add bleach. I plan to do my own data collection on this for my setup but I was wondering if I only get a few points each scenario if its realistic to assume a straight line graph?

Related question...Does the approx 15 degree water temp swing I may swim in across seasons impact the ORP reading? I've read temperature matters but does it even need to be taken into account for this swing?

Pool Calc question......Does anyone have values at very small levels what I need to move FC and PH in say a 1 or 5 gal bucket??? The pool calc does not go out enough decimal places for my unique needs. I can just divide backwards but I don't know how much rounding is already done.
 
It won't be linear based on FC level. It will be closer to logarithmic where every doubling of FC results in some mV increase in ORP, say 35 mV. A 15F temperature increase can drop the ORP by about 20 mV. So yes, both pH and temperature need to be taken into account.

As for bucket amounts, if you're a masochist, you can use my Pool Equations spreadsheet changing the volume as appropriate.
 
My Pool Calculator does a fair bit of rounding. The best solution is to tell my Pool Calculator that you have 1,000, or 10,000, times as much water as you actually have and then divide the result by 1,000, or 10,000. This is simplest to do with using metric units instead of standard units.
 
Anyone following my posts and looking for numbers to support Chemgeeks PH to ORP advice please see this helpfull link I found. Project going welll, just found out that unfortunately my used with little data PH/ORP controller/sensor appears to only do PH....Back to more parts. Its printed right on the controller (Oakton PH/ORP) but does not seem to have a jumper or way to use it as ORP (too old for manual online).

Good reading if you want to understand more about sanitation levels and reading them with a sensor (if you just want to see the chart of relationships see the last page).


:shock: http://www.sbcontrol.com/orppaper.pdf
 

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I've used that chart of relationships in my spreadsheet here under "Approximate Chemtrol ORP (mV)" at line 378 of the spreadsheet. I also have a data fit for "Approximate Oakton ORP (mV)" at line 379 and another for Sensorex at line 380. In other words, sensors are not consistent, even measuring the same water. Not only are their absolute readings different, but even worse is that their mV increase for every doubling of chlorine concentration varies and their variation with pH is different as well.

I wrote more about ORP sensors and their inconsistencies in this post a while ago and I developed the Oakton formula from data summarized (graphed) in this post.

Richard
 
chem geek said:
In other words, sensors are not consistent, even measuring the same water. Not only are their absolute readings different, but even worse is that their mV increase for every doubling of chlorine concentration varies and their variation with pH is different as well.

Richard
Click to expand...
THIS is why I am not a fan or ORP control for residential pools. There is too much difference in sensors and I suspect quite a bit of the difference (and accuracy) is price related! I have found nothing so far to change my mind on this!
 
Waterbear or Chemgeek(or anyone with similar ORP sensor experience):

Per your and ChemGeeks advice I will see differences in the ORP values based on where I'm at for the FC and who made the equipment/sensors. But will I get somewhat consistent values on the same testing gear? If I know from my test kit and my CYA/FC level that say a FC of 5 is what I need and the corresponding ORP value is say 700 on my setup, can't I just set my chlorine injector to come on below 700mv?

Or are you saying real world the readings vary too much on the cheaper sensors/controllers with PH and temp changes and repeatability on the same water? I realize from charts I've seen that these do come into play so I would need to be cautious of this when i decide what number to dial in for the relay running the chlorine pump. I know cleaning/calibration also ties in but not needing super precise numbers couldn't I just dial it in once a season? For my needs drifting a few mv I dont think would impact much as long as I'm reading the same value each time the same sample of water.

Information on this is really appreciated before I spend anymore money on my gear. If this is getting too deep trying to do this with low-end ORP sensors and controllers I will just tweak my pump manually and forget trying to tell it when it needs to run. :whip:
 
For a given piece of ORP equipment in a given set of water, it usually measures fairly consistently from what most people have reported. However, there are items such as the amount of hydrogen in the pool that can throw off the sensor (hydrogen bubbles coming from an SWG and saturating the water, for example). So, at best, ORP sensors can be seen as chlorine level trigger sensors using fixed setpoints that you predetermine for your pool carefully measuring the FC, pH and temp.

There are also specialized membrane-based hypochlorous acid (still voltage-based) sensors but it's not clear how reliable or accurate they are. The gold standard for electronic chlorine measurement is the amperometric sensor that measures current where a membrane is used for selective diffusion of hypochlorous acid. The amount of current from an applied voltage is related to the hypochlorous acid concentration based on the diffusion rate of hypochlorous acid through the membrane. It is only pH dependent, requiring a pH sensor, if you are trying to calculate hypochlorite ion as well or have CYA in the water and want to determine Free Chlorine (FC). These sensors are not cheap -- typically costing thousands of dollars.

Richard
 
IMHO, it is possible to set a peristaltic pump to deliver the correct amount of liquid chlorine to maintain a pool without resorting to ORP or pH controllers. You would still need to test the water on a regular basis but it's a much simpler way to do it. In a commercial application with varying bather loads there is some advantage to ORP control but you are now talking about more sophisticated systems that are quite costly and also have the manpower available to maintain and calibrate them. My feelings is that for a residential pool you are making things more complicated than they need to be by adding controllers for chemical feeding. If you want to spend money on automation I feel it is better spend on automating valves by using acutaltors and having remote control of such things as lights and heaters and pumps.
My 2 cents.
 
Thank you WaterBear and Chemgeek....I beleive I will heed to the advice to integrate the ORP stuff later......I need to put my pool pump on a timer anyways (as part of the project) and may get creative with a second timer in case I want to dump a higher rate over a shorter time at night opposed to just leaving it on very low flow throughout the pool pumps cycle...I dont have that much deviation in bather load so I will see if I can just do it, and monitor a few times a week to see if I'm gaining/lossing ground on FC level (initially I'm sure it will be 2-3x's a day logging data till I get it somewhat dialed in).....THANKS for including real world advice!!!!!!!!!!!!

BTW, anyone following this thread, I found three threads discussing ways about automating the injection of chemicals as reference (some of my answers were in there, the more I read this site the more I find data I need inside another thread):

homemade-acid-or-chlorine-injection-system-t4174.html
building-chlorine-injector-t1850.html
about-passive-delivery-of-liquid-chlorine-when-away-t9894.html
 
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