How long does it take for Chlorine to evaporate?

I just started to make some experiments with Calcium Hypochlorite to keep my res clean and dead (sterile).
I bought ORP meter which should reveal the oxidation (killing) potential of the water. I tried different measures in different times. The goal is to find out how often and what dosage we should add a pool shock to keep the res constantly sterile.

What I used:
-RO water (0,01EC)
-Calcium Hypochlorite 70% (aka pool shock)
-ORP/PH meter ADWA ad14 (-1000mV - +1000mV)
-nutes - AN 3part

Theory:
ORP meter is sufficient for this type of measurement. It indicates the value in "mV". Negative value for living res, positive value for dead res. Hydroponic ORP value should be c.+600mV for keeping the res at 99% dead.
I used Chlorine as an oxidation agent in this experiment. Chlorine in water is could be in free form (hypochlorous acid and hypochlorite ion) or combined form (chloramine). Free form is the most reactive, chloramine is less reactive, but it still is reactive. Chloramine forms when free chlorine is reacting with nitrogen, especially in amonium form (NH4+).

The second thing which is playing against us is evaporation of chlorine and chloramine.
How fast? When is our res not so killing?

There are my results:
I started with clean RO water and adjust the PH to 5,5 (as it is very important for this test to ensure the PH is stable and the same during the test - bcs the PH level affect the ORP level).

This PH stabilized RO water had 320mV - it's not sterilizing the funghi (pythium, phytophtora, etc.)
Then I add 1,5ppm of chlorine. It skyrocketed the ORP to 730mV! (still not reacting with amonium)
Next step was adding the nutes. I added 0,5EC of 3part AN nutes and the ORP level dropped immediately to 603mV. 10min later it dropped to 580mV, 20min later 570mV. I pour off 1l separately as a second sample for measuring. Second sample was sitting undisturbed.

570mV should be OK, so I made a flood and drain cycle, measured the ORP of drain water and res tank water separately. ORP was still falling down. 517mV an hour later. Doesn't matter if it was drain or res tank.
At this time I started to add premixed chlorine with RO water solution to the res tank. It ended at 600mV, but I had to add another 2,5ppm of Chlorine to reach this level.

After 15 hours I measured the res tank again - 390mV.
Second sample with 1,5ppm of chlorine was 390mV too.

This lead me to find out what are the chlorine evaporation times and I found out this chart:
WATER TREATMENT QUANTITY IN GALLONS / LITERS 1 PPM OF FREE CHLORINE / 1 PPM OF CHLORAMINE
Undisturbed 10 gal / 37.85 liters up to 55.3 hrs up to 173.4 hrs
Circulated 10 gal / 37.85 liters up to 9.6 hrs up to 70 hrs
Circulated, Aerated 10 gal / 37.85 liters up to 9.2 hrs up to 67.6 hrs
Boiling 10 gal / 37.85 liters up to 3.7 minutes up to 64.8minutes

As you know - hydroponic res tanks are circulated and aerated. This means 1ppm of chlorine is completely out after 9,2h and 1ppm of chloramine after 67,6h. They say (in that article) you should multiply the hours by number of ppm present in your res tank. But as you see, 15h later, there is just a trace amount of reactive chlorine present in the water.

Conclusion:
As a next step, I will try to add more chlorine and no other nutes to eliminate reacting with amonium. But I guess, it's just a chlorine evaporation what dropped ORP level that much. Why would in another case 1,5ppm and 4ppm of chlorine ended at the same ORP level?

Is adding calcium hypochlorite worth it when it evaporates that quickly?


I'm going to make few more experiments, so I will keep this thread up.

An ORP measurement provides signals about what factors might be inhibiting the chlorine’s ability to oxidize. Perhaps the chlorine is tied up with phosphates from nutrients when the ORP is dropping? This doesn’t mean the chlorine can’t do its job, because it will break free as needed to oxidize and sanitize. Just a guess. Thing is there are many factors that can cause ORP readings to fluctuate while the PPM of free chlorine is stable.

If you water contains only chlorine and not chloramine, you can let it sit for 24 hours and the chlorine will dissipate into the environment.

MyFloridaGreen360 said:

If you water contains only chlorine and not chloramine, you can let it sit for 24 hours and the chlorine will dissipate into the environment.

Click to expand...

That's not what the OP is getting at. He wants to quantify the amount of time that pool shock is effective before it needs to be supplemented. (I think thats what he's after anyways LoL)

I don't have any fancy answer or science, but I've used shock to sterilize my res for over 4 years in the summers when its hot, in the winter I don't bother. I had read when I researched it that it can take any where from 24 hours-3ish days. I usually add a dose every 3-4 days just to keep things clean, and not be concerned with over doing it.

How are you measuring free chlorine and total chlorine? I tried some strips, but they didnt work for crap. The ones I bought wouldnt read anything until the concentration was over 20 PPM.

I have some sort of brown crap in my HPA system. I have to add at least 4 to 6 PPM of chlorine pretty much every day fr several days to get it to die back. If I stop treating, it comes back quickly. The main problem the brown crap is causing me is wild increases in PH. Plus, it kills off fuzzy hairs on the roots. Unfortunately, the hi levels of chlorine also kills off fuzzy hairs.

Have you considered using uvc sterilization for your res?you can purchase an aquarium sterilizer that you can leave in your res with a timer to cycle it as needed.no change to orp or water chemistry and it will kill any pathogens in your water. I have read that it may cause some drop out of iron when used in a res,i have been using a whole home inline sterilizer with great results but have not used one inn my res so don't really know if the iron dropping out of solution is an issue or not. Certainly helped a persistent pythium issue i had in my food and drain set up, much more so than the standard chlorine well shock that i had tried

Well, I got new observations, but first I have to respond to all of you.

Renfro said:

An ORP measurement provides signals about what factors might be inhibiting the chlorine’s ability to oxidize. Perhaps the chlorine is tied up with phosphates from nutrients when the ORP is dropping? This doesn’t mean the chlorine can’t do its job, because it will break free as needed to oxidize and sanitize. Just a guess. Thing is there are many factors that can cause ORP readings to fluctuate while the PPM of free chlorine is stable.

Click to expand...

-Chlorine can react with amonia nitrates (urea) and make chloramine instead. This is clear and we also know, that chloramine is less reactive than free chlorine. ORP should read this reactiveness. Yes, many factors could fluctuate ORP readings (such as temperature or PH) - but they are stable in my case. What is not stable is evaporation and reaction.

Thundercat said:

I don't have any fancy answer or science, but I've used shock to sterilize my res for over 4 years in the summers when its hot, in the winter I don't bother. I had read when I researched it that it can take any where from 24 hours-3ish days. I usually add a dose every 3-4 days just to keep things clean, and not be concerned with over doing it.

Click to expand...

-Yes, this is what many growers do. But I wanted to look more inside and know what is happening and if I am doing it right. As everyone is using different nutrients, different technique and different conditions - ORP level should be the same in everyone's case.

Larry3215 said:

How are you measuring free chlorine and total chlorine? I tried some strips, but they didnt work for crap. The ones I bought wouldnt read anything until the concentration was over 20 PPM.

I have some sort of brown crap in my HPA system. I have to add at least 4 to 6 PPM of chlorine pretty much every day fr several days to get it to die back. If I stop treating, it comes back quickly. The main problem the brown crap is causing me is wild increases in PH. Plus, it kills off fuzzy hairs on the roots. Unfortunately, the hi levels of chlorine also kills off fuzzy hairs.

Click to expand...

-I am not measuring free chlorine or combined chlorine levels. I am measuring oxidation-reduction potencial. It is simply saying how much your water is pathogen killing. As you know what ORP level your water with nutrients is, you can easily say how much of active chlorine (not important in which form) is still present in your water. When you have a starting nutrient solution of 300mV, then you add 4ppm of chlorine to make 650mV and a day later it is 400mV - you know, that there is still a bit more than 1ppm of active chlorine (most probably in chloramine form).

Mountainlife420 said:

Have you considered using uvc sterilization for your res?you can purchase an aquarium sterilizer that you can leave in your res with a timer to cycle it as needed.no change to orp or water chemistry and it will kill any pathogens in your water. I have read that it may cause some drop out of iron when used in a res,i have been using a whole home inline sterilizer with great results but have not used one inn my res so don't really know if the iron dropping out of solution is an issue or not. Certainly helped a persistent pythium issue i had in my food and drain set up, much more so than the standard chlorine well shock that i had tried

Click to expand...

UV sterilization is good just to sterilize the res tank. But the whole disaster is happening directly on the roots. It could work to lower the amount of spores and bacteria, but it is also reacting with chelates and could make a micro nutrient deficiency. But if it works for you - it's great. I have a large setup, so it could be more expensive than all the ORP stuff.

New observations:
I tried to keep my ORP level at +-600mV, but a day later it was 400-450mV again. Doesn't matter if I add 1,2 or 3ppm the day before.
I was also searching google and was trying to find some researches in which people tested needed ORP level to kill any hydroponic pathogens and I have to say, that I was wrong with that +-600mV statement. It is far more we have to reach to kill pathogens - up to 800mV!!! But I was able to reach just about 630mV with 4ppm of chlorine.

The rule of 3-4days with 3-5ppm of chlorine is actually pretty close to what is best to do. But you (me) need to find the correct ppm level.
Also 3-4days could be perfect to ensure there is no combined chlorine still present in your nutrient solution.

foliage2018 said:

This lead me to find out what are the chlorine evaporation times and I found out this chart:
WATER TREATMENT QUANTITY IN GALLONS / LITERS 1 PPM OF FREE CHLORINE / 1 PPM OF CHLORAMINE
Undisturbed 10 gal / 37.85 liters up to 55.3 hrs up to 173.4 hrs
Circulated 10 gal / 37.85 liters up to 9.6 hrs up to 70 hrs
Circulated, Aerated 10 gal / 37.85 liters up to 9.2 hrs up to 67.6 hrs
Boiling 10 gal / 37.85 liters up to 3.7 minutes up to 64.8minutes

As you know - hydroponic res tanks are circulated and aerated. This means 1ppm of chlorine is completely out after 9,2h and 1ppm of chloramine after 67,6h. They say (in that article) you should multiply the hours by number of ppm present in your res tank. But as you see, 15h later, there is just a trace amount of reactive chlorine present in the water.

Click to expand...

Does this mean we can apply Calcium Hypochlorite dosage daily to maintain sterile environment?