Calibrate DIY chlorine color tester

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Day 2 of using the new color sensor and am really confidant with the reading that I am getting.

A late afternoon sample gave me a reading of 2.45 ppm. Again we spent more than 3 hours in the pool today, 4 people, lots of sunblock, etc.

In addition to now having the LCD display the Green sensor reading, and the ppm value, next I want to add a calculation and display for the exact volume of cal-hypo to add to reach my target FC ppm value.

The pool calculator tells me, for my size pool, that 1000g cal-hypo raises FC by 17ppm.
So the Formula will be :
Code: 
( (  FC_target - FC_now ) / 17) * 1000

The solar coils again had the pool at 32 Celcius ( 89.6 F ) by 9am, so am considering re-naming it to the oversized hot-tub.

Added 2 waterproofed digital temperature sensors to the pool water and the solar coil return pipes, and connected to the Arduino board and LCD screen. Average was 32C pool water and 35C return from coils ( air temperature 29C ). With the brisk speed of the water thru the coils, the joules of energy entering the pool must be some good numbers.

Am looking forward to testing again over the next few days.

Next week when everyone is back at work, I want to take the complete unit to the local laboratory and ask the technical manager to make me some control samples of different pH values. I can then test them on site using the reagents that I have, and create a calibration table like I did for the DPD colors. Once that's done, the visual comparison to the printed color chart is history, and I am in control.

Shout if anyone is interested in the findings for the pH testing, and I will update the thread once done.
 
Day 6 and really happy.

It's been 6 days since I started using my DIY color analyzer for the DPD tablet test tube.

In all cases, I have used the HTH water tube to measure the 13ml of sample water, calibrated the sensor, and then added the DPD tablet.

And in every case, I have noticed the pink color, compared to the printed chart, looks darker than the true reading.

This has made me realise that in the past, I was visually seeing, for example, 2ppm but in reality it was only, say, 1ppm. As a result, I was previously adding too little cal-hypo and not reaching the 4ppm that I should have for my CYA level.

After 2 days of starting to use the sensor, the very light algae that was often in the corner by the steps had completely disappeared.

Considering that we have had a week of 30 celcius and 3 or 4 people, with sun-block, in the pool for 2 to 3 hours a day, I full accept the FC readings that I am getting. Afternoon readings are around 2.422 ppm ( using the calibrated values posted earlier ) and I add cal-hypo to increase to 4 ppm.

The quality of the water also appears to have increased. Visibility underwater using a mask at the deep end, I can see the texture of the fibreglass at the other end, 8 meters ( 26 feet ) away.

Next will be the pH calibration.
 
jblizzle said:
If you were seeing ANY algae, then you should follow the SLAM Process to "sterilize" the pool. You likely still have low level algae growth that may not be visible, but is certainly consuming FC.
Click to expand...

Thanks for the advice Jason. Much appreciated.

Just a question : shouldn't the slam process first start with an overnight test to actually determine if it is required ?

Also, I didn't see anything about using the pool during the slam ?
 
Well visible algae fails one of the tests which means you should SLAM. It also does not sounds like your water is crystal clear.

Generally it is best not to swim while in the SLAM process ... Although the active chlorine level is still less than many public unstabilized pools.
 
I usually recommend running the pump overnight while doing the OCLT just to ensure everything is circulated, although others think it should not matter (although you would need to run the pump at least an hour before you test in the morning). BTW, I also think it is a good idea to raise the FC up to at least around 10ppm for the OCLT. If you only started with 4ppm, then a 1ppm drop is pretty significant and maybe only 0.5ppm drop should be acceptable.
 
jblizzle said:
I also think it is a good idea to raise the FC up to at least around 10ppm for the OCLT. If you only started with 4ppm, then a 1ppm drop is pretty significant and maybe only 0.5ppm drop should be acceptable.
Click to expand...

Many Thanks for the advice.

The above statement, although most likely true based on your experience, I do not understand.

My thinking tells me that if there is a problem like algae, that it would consume 'x' amount of chlorine ( in ppm ) over a time period. Why then would it matter if you start the test with 4ppm or 10ppm ?
 
I see what you are saying, but I think the ratio of the CYA level to the FC level comes into play.

The OCLT procedure was written with the assumption that you are in the SLAM process with the FC up at SLAM level to see if you are ready to stop and that is where the 1ppm came from. I recall a discussion that if the FC is well below SLAM level, then perhaps the OCLT should only be a "pass" if you lost 0.5ppm or less instead of 1ppm. But, this discussion never made it into any documentation in an effort to keep things simple.
 

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