Liquidator and Chlorine/CYA Chart

[mrafal]

So now that we have continuous infusion of chlorine using the Liquidator, can we safely use the SWG levels for chlorine rather than the non-SWG levels?

I generally run my pump (and hence the Liquidator) from 9:00AM to 6:00PM, so I'm feeding chlorine continuously during bright daylight. Moving towards the lower SWG numbers would save a good deal of bleach.

Marc

 

[duraleigh]

I am currently doing that. I haven't made a big deal of it because it's really just an experiment but I am running my FC around 2ppm with a CYA of 60. The water has been sparkling to date (6 weeks) and my chlorine use is pretty small.

My pump is timed in three cycles (4 hr, 3 hr, 3 hr) with the heaviest run time obviously during the peak afternoon sun and the least run time at night.

So far so good.

 

[chem geek]

Marc,

The answer is "I don't know". We never definitively determined why the SWG pools can safely operate with an FC that is around 5% of the CYA level compared to the minimum recommended of 7.5% of the CYA level for manually dosed pools. One factor is the continual dosing and more consistent FC level, but another factor is that there is super-chlorination at up to 80 ppm FC between the plates in the SWG cell and that will kill free-floating algae rather quickly. Only a portion of the water through the SWG is exposed to that high level of chlorine, but it might be a factor.

Carl has mentioned that Ben's chart minimums had some slack in them accounting for manually dosed pools and the fluctuation of FC that occurs in such pools so it is quite possible that an FC of around 5% of the CYA level may work well for pools using The Liquidator. This is just something for people such as yourself [EDIT] and Dave, who I see just posted [END-EDIT] to try out and report back and when we have enough of these reports then we can make a more definitive recommendation.

Richard

 

[mrafal]

Richard,

I've been running at the higher levels, but will trim it down and see what happens. It occurs to me that the Liquidator superchlorinates the water on top like the SWG, though perhaps not at quite as high a level.

Awfully complicated for such a simple device.

Marc

 

[revstriker]

So if my FC range is between 3 and 6 (for instance), are you suggesting that I would use less chlorine if I maintained it at 3 than if I maintained it at 6? So if the UV from the sun is burning off some of my chlorine, would it burn off the same amount at 3 or 6 (assuming my CYA was the same), or does it burn off a percent of the total?

 

[JohnT]

It occurs to me that the Liquidator superchlorinates the water on top like the SWG, though perhaps not at quite as high a level.

It raises it to a very high level in the tank, but the amount of pool water that actually flows through there is very small compared with a SWCG.

 

[mrafal]

So if my FC range is between 3 and 6 (for instance), are you suggesting that I would use less chlorine if I maintained it at 3 than if I maintained it at 6? So if the UV from the sun is burning off some of my chlorine, would it burn off the same amount at 3 or 6 (assuming my CYA was the same), or does it burn off a percent of the total?

My understanding is that the amount of burnoff for a given CYA level is a percentage of the chlorine level. So if you drop from a FC of 6 ppm to 3 ppm, the absolute amount of chlorine consumed will be lower by about 50%. I'm guessing that is only approximately true and the real savings will be somewhat less. Murphy says these things are always non-linear in the wrong direction.

Marc

 

[chem geek]

As Marc points out, the sunlight breaks down chlorine as a percentage of the total (all else equal, such as CYA level). So a lower FC has a lower absolute FC loss. However, sunlight is not the only source of chlorine usage so as Marc says you will find that 3 ppm FC doesn't lose half of what is lost at 6 ppm FC since some loss isn't from sunlight. Some of the chlorine loss will be oxidizing ammonia/urea/organics and though this will be slower at the lower chlorine level, much of it will still occur within the day so will still be seen as a fixed absolute daily FC loss somewhat independent of FC level.

Richard

 

[Rangeball]

It occurs to me that the Liquidator superchlorinates the water on top like the SWG, though perhaps not at quite as high a level.

It raises it to a very high level in the tank, but the amount of pool water that actually flows through there is very small compared with a SWCG.

But as posted above, isn't the amout of pool water that actually flows through the blades of an SWG also very small?

 

[mrafal]

It occurs to me that the Liquidator superchlorinates the water on top like the SWG, though perhaps not at quite as high a level.

It raises it to a very high level in the tank, but the amount of pool water that actually flows through there is very small compared with a SWCG.

Does anyone know the scale for the flow indicator that comes with the Liquidator? I'm guessing the range must be some fraction of a gal/min.

Marc

 

[revstriker]

Marc/Richard: Thanks. That's what I thought from reading the post, but I wasn't sure.

 

[JohnT]

It occurs to me that the Liquidator superchlorinates the water on top like the SWG, though perhaps not at quite as high a level.

It raises it to a very high level in the tank, but the amount of pool water that actually flows through there is very small compared with a SWCG.

But as posted above, isn't the amout of pool water that actually flows through the blades of an SWG also very small?

Yes, but the speculation is that there is enough chlorine produced that the entire volume of water in the cell is highly chlorinated.

 

[chem geek]

Well, the entire flow through the cell can't be at 80 ppm or that high in FC or else it would come out of the returns that way and require very short on-times. In practice, a properly sized SWG probably outputs at an FC that is about 4 ppm higher than the pool water such that a 2 ppm per day usage would mean roughly 50% on-time during one turnover of the water.

An SWG manufacturer (I think it was PoolSean, but I don't recall) said they measured the chlorine level between the plates at 80 ppm, but not all water flows between all plates. There is some flow around the outside of the plates and water near one plate will be low in FC and high in pH while the other plate will be high in FC and low in pH. It should be noted that the water near the chlorine generation plate is not only high in FC, but in active chlorine level (hypochlorous acid) as well and that chlorine gas bubbles downstream also have a high FC and active chlorine level for a short time until the chlorine is able to combine with CYA (it's fairly fast, but not instantaneous).

So who knows what percentage of water is exposed to high chlorine levels in an SWG cell. Perhaps it's only 10% or less. Basically, The Liquidator operates with an on-time that is longer than that of an SWG -- the LQ is on whenever the pump is on. So since only some of the water flows through the LQ, this means the water leaving the LQ has to be at a fairly high FC, but when mixed with the regular water after the pump the net result is a lower FC than coming out of an SWG. The main difference is that the LQ water has a lower active chlorine concentration lowered by CYA while in the SWG the freshly generated chlorine will be all active for a very short while. But this is all just logical speculation.

Richard

 

[Rabbit]

I'm no expert on this in any stretch. That being said I found it logical that the 70+ (I measured the top of my LQ) ppm chlorine concentration w/ 10% bleach or much higher with 12.5% hitting a 2 inch pipe in my case would result in the water in the small area of pipe getting fairly well chlorinated for at least a short while. Once it hit the pump skimmer it would dilute down a bit (but still much higher then the pools FC) once it hit the filter it would be diluted even more (but still higher then the pools FC). It would then have to travel the distance to get to the output jets where it would be diluted in the thousands of gallons of water and start to be destroyed by the sun and other things. My pump can turn over my pool water more then once a day based on it's specs. So pretty much all the water in the pool gets subjected to this higher chlorine level at least once a day.

Bottom line is I don't see how the levels of chlorine wouldn't not be much higher in the skimmer basket, filter and outflow pipes and not help do something.

Again I'm no expert, so feel free to find flaws in my thinking.

 

[JasonLion]

A SWG runs about half as long, since they cycle on and off (a 50% setting seems like a good average guess). So a SWG is injecting chlorine at something like twice the rate for half as long (though the actual ratios will vary depending on the percentage setting on the SWG). Other than that, the effects should be similar.

Since they are within a factor of two of each other, I would expect the behavior to be similar, and the SWG target FC levels to work with the LQ. However, half the rate isn't exactly the same, and the chemistry inside a SWG cell is rather more complex than the chemistry inside a LQ. Because of that, there is at least a chance that they behave differently. We simply don't have enough experience with real world operation to be sure either way.

FC lost to sunlight is (more or less) a fixed percentage of your current FC level. Lower FC levels mean less chlorine lost to sunlight.

 

[Rabbit]

I figure it has to be of some benefit injecting 70+ ppm chlorine in to my main pump inlet pipe compared to say dumping in bleach once a day and having it sit in the sun in a much more diluted state. In my case I'm even using all black 3/8 inch ID line from the LQ, so the sun is not even hitting it until it gets to the pool. My CYA is around 58, so I'm going to try to run at 3 ppm for a while and see what happens. The second I start to see any green I'll back down on my assumptions. So far the LQ is working wonderfully. I've switched to 12.5% HASA and I've noticed a major increase in FC based on flow. I actually had to turn the thing down vs 10% as my FC was just climbing and climbing.

 

[chem geek]

I'm no expert on this in any stretch. That being said I found it logical that the 70+ (I measured the top of my LQ) ppm chlorine concentration w/ 10% bleach or much higher with 12.5% hitting a 2 inch pipe in my case would result in the water in the small area of pipe getting fairly well chlorinated for at least a short while. Once it hit the pump skimmer it would dilute down a bit (but still much higher then the pools FC) once it hit the filter it would be diluted even more (but still higher then the pools FC). It would then have to travel the distance to get to the output jets where it would be diluted in the thousands of gallons of water and start to be destroyed by the sun and other things. My pump can turn over my pool water more then once a day based on it's specs. So pretty much all the water in the pool gets subjected to this higher chlorine level at least once a day.

Bottom line is I don't see how the levels of chlorine wouldn't not be much higher in the skimmer basket, filter and outflow pipes and not help do something.

Again I'm no expert, so feel free to find flaws in my thinking.

It doesn't work the way you describe. Assuming that the output of the Liquidator goes into a single inlet pipe into your pump, then it gets FULL dilution at the full flow rate of your pump. You are correct that the small area of the pipe near the injection point gets a higher level of chlorine, but very soon after that it gets mixed up and diluted with the turbulent water flow, especially by the time it hits the pump basket. The flow rate out of the Liquidator is on the order of less than one gallon every minute (see this post) while the flow rate through the pump is 40 GPM or thereabouts depending on your pump speed and system setup. So the dilution rate is on the order of 1/40th to 1/80th or even more. Basically, the net result is an increase in FC by the time the water hits the pump basket of only 1-2 ppm which makes sense since that's about the amount of chlorine that needs to be added into the pool over the duration of time the pump is running, assuming it is running mostly during the day.

In other words, the output of the Liquidator does not produce high levels of chlorine through the rest of the system. The fact that it hits more water volume in areas like the filter is exactly compensated for by the lower flow rate through the filter -- there is no additional dilution in the filter -- the main dilution occurs near and just after the injection point between the LQ and the pump basket. The way you need to look at it is how long it takes for injected chlorine to become fully diluted across a cross-sectional area of water flow going through the system. Realistically, this happens as it travels in the pipe and hits the pump basket. I doubt very much that the water leaving the pump basket and going into the pump is not essentially fully diluted (mixed). Even if it wasn't, the average FC across a cross section will only be 1-2 ppm FC higher than the original input water from the pool -- the only issue is whether some areas of the cross section are still at much higher FC levels and I'm saying that they aren't.

Richard

 

[DLSDO]

I figure it has to be of some benefit injecting 70+ ppm chlorine in to my main pump inlet pipe compared to say dumping in bleach once a day and having it sit in the sun in a much more diluted state. In my case I'm even using all black 3/8 inch ID line from the LQ, so the sun is not even hitting it until it gets to the pool. My CYA is around 58, so I'm going to try to run at 3 ppm for a while and see what happens. The second I start to see any green I'll back down on my assumptions. So far the LQ is working wonderfully. I've switched to 12.5% HASA and I've noticed a major increase in FC based on flow. I actually had to turn the thing down vs 10% as my FC was just climbing and climbing.

Same "problem" Rabbit. Now I am turning down my flow due to great flow and higher than needed FC based on my CYA. Its a good problem.

 

[Rabbit]

So the question is, how is taking 70-80 ppm chlorine injected in to a pipe from the LQ that much different from taking 70-80 ppm chlorine flowing from an SWG. The dilution rate would appear to be about the same. Granted the SWG might have higher levels for a millisecond or so vs the LQ or perhaps a larger surface area. I also see that even if the FC in the filter is 1-2 ppm higher then the rest of the pool it would still have a benefit to the sanitation of your water. Now as I understand it the more CYA you add to the system the slower the kill rate of the chlorine, so that may have somewhat of a cancellation effect. The same one would think would also hold true to a lesser degree for the SWG. The LQ has already started to mix with stabilizer before it hits the pipe where the SWG has not.

You have to look at it this way, the PPM in the whole pump system has to be higher then the rest of the pool or the FC would never even stabilize. The same would be said about a floating distributor, the chlorine right next to it would be much higher then the rest of the pool.

I think we really need some trial and error on this. I don't feel it can be just shut down as the logic says otherwise. I also see how an SWG would do better and won't dispute that fact. The LQ on the other hand based on logic should fall somewhere in the middle of manual adding and the SWG.

 

[JasonLion]

What really matters at this point is empirical testing. We can theorize about flow rates and boundary layers all we want, but it won't prove anything. We still don't understand why lower FC levels work with SWGs, so we can't use theory to prove that the same conditions hold in a LQ system.

Because we are trying to make recommendations that work in nearly all situations we need a lot of empirical testing in many different pools. The more people who are interested in experimenting with setting their LQ to the FC levels normally recommended for SWG system, the faster we will be able to have an answer.