Ideal Salt Level Pool Pilot

[smallpooldad]

What is the ideal level of salt ppm for the Pool Pilot? The manual states 2500 to 3500. Is 3000 the optimum for chlorine production?

What, if any, are the benefits or negatives of running it at either extreme, 2500-3500? I do realize that lower levels produce a less corrosive enviroment and higher more corrosive; theoretically one could use less calcium with the lower number. The second consideration is that bees are attracted to the pool when the salt level is higher. I am told but do not know if it is correct that bees are attracted to salt, from my experience this is true. I can only suppose that they use the salt, as do horses, as a salt lick. Are there any other considerations?

I love this unit, SC-60, it maintains 6 ppm of chlorine and holds it there most of the day in 10,000 gal pool running 4 hours per day at level 3. Level 2 produces around 4.5 ppm.

The reason we go to 6 ppm chlorine is to control mustard and black algae, creating an HOCL as ppm of 0.080 at a CYA of 35 and pH of 7.5.

Any help would be appreciated.

[Poolsean]

You're not going to have a problem lowering your FC to 3 - 4 ppm.
That's a different topic altogether.

To answer your question, the Pool Pilot will operate properly from 2500 ppm on up. 3000 ppm is better but higher is even better. It allows the power supply to run cooler (internal temperature-wise).

When you run lower than 2500 ppm, you reduce chlorine production and can get to the point of cell wear.
Running higher levels of salt doesn't generate more chlorine, but again, helps the Pool Pilot run cooler, which always helps electronics.

[smallpooldad]

Sean,

You are so fast.

Great informative reply, I wished they had mentioned that in the manual.

As regards Chlorine levels for my pool and my neighbours higher is definetly better.

Thank you this was very helpful.

Aloha

[waterbear]

You are running your CYA very low for a salt pool. Try raising it up to aobut 70 ppm. You will find that your pH becomes less likely to rise since you will be able to run at a lower power level/output percentage and you will also find that a FC level of about 4 ppm is more than enough to control ALL forms of algae.

[smallpooldad]

Waterbear,

Thank you for your kind help.

I would agree that on most parts of the mainland 4 ppm chlorine might be fine, although some on this forum have stated numbers between 4 and 6 work better for them. Being further south at a latitude of 21.18 (Miami is at 28.10) it seems as if our algae, especially black algae, is of a stronger type or is benefiting from the extra UV radiation.

As black algae can only be killed, or maybe only controlled from growing, by a residue sitting on it, unlike other floating types which get wacked by the SWG. The poolperson who installed the generator stated that SWG pools in Honolulu have a tendency to get black algae unless they keep the FC at 5-6.

There are many different types of Black Algae I could assume that our type could be called "The Hawaiian Super Black Algae"!!!

I am not sure all algae can be killed by FC of 4, the killing part is the HOCL % this percentage is a far more important number than FC and that is dependant on a combination of pH setting , the amount FC, and the level ppm of CYA. The only way I know how to calculate HOCL% is to use the "PoolEquations" Excel spreadsheet; so it is not very user friendly for the general public.

Even then we now know that some forms of life can live in impossible area such as deep sea trenches, sulfur springs, etc. The use of "ALL algae" might better replaced by "most known algae". Here is a link that explains the many species:

http://en.wikipedia.org/wiki/Blue-green_Algae

At 4 ppm it slowly starts to raise its ugly head; at 6 ppm there is no sign of it. My Pool Pilot is set to an ORP of 700, power level 3, which produces and maintains a reading of 6 ppm FC. It runs for 4 hours per day (electricity is .35c KwH) so the shorter the better. The pool is 10,000 gals and has a flow of 55 GPM, so the turn is 1.32. The SWG cell itself does not run 4 hours per day as often it has reached 700 ORP even before it starts up. The pool is covered so this helps, it also assists in keeping the pH at 7.5 with little acid usage which is automated. If the pool were uncovered it might use more acid.

The HOCL % therefore with a CyA of 35 ppm is 0.080% (chem geek states that an HOCL % over 0.075 kills most known marine varities). Raising the CyA would lower this HOCL %, as would lowering the FC below 6, which what we are most interested in acheiving as it seems at this level can only be reached by a combination of pH 7.5, CyA at 35, and FC of 6. If we raised the CyA level we would need to produce a higher chlorine level and that would require the SWG to run longer. The aforementioned combination of numbers seem to give the optimum results, the pH level of 7.5 is good for the eyes and the chlorine is still at safe levels. Pool Pilots Manual states this is OK so long as one is digitally automatically feeding the acid.

My friend's pool (20,000) gals runs for 8 hours per day. He has a Jandy Autopilot 1400, it is turned up to 81%, the pool is uncovered and his pH rises by about from 7.4 to 7.6 each day, he has, as is mine, an Alk of 80, he does not use borax, I do. His FC is maintained at 6, and again no black algae. We plan on automating his acid feed.

I believe there are no hard and fast rules but if you saw how fast mold grew in Hawaii I think it would be easier to understand. I think that latitude and humidity also play a part in what variety of algae one gets. Hope this explanation helps in understanding why we are so neurotic over FC levels.

Finally I have to admit to being a little confused as I am not a biologist or biochemist, maybe Chem Geek can clarify this, why does one have to shock a pool at say 25 ppm of chlorine if 4 or 6 ppm of chlorine (HOCL% dependant) is killing most known algae? What further benefit does the shock have? I realize that the levels do have to elevated somewhat as the chlorine is used up in destoying algae but by why so high at say 22, or 25, or 29 ppm?

[waterbear]

Ok, did not realize that you had a Total Control system. That's a different animal completely. As far as the level needed to keep away black algae it's not so much the FC as the ORP reading. 700 mv is on the low side of the usual range. In your climate I would think an orp reading closer to 800 mv would be better, particularly when trying to kill black algae (which is really a blue green algae or cyanobacteria) .
In marine aquairums ORP readings can accurately predict the type of algae that will grow. When the ORP is low you will get red and blue green algae (usually in that order). As ORP continues to rise (usually from the use of ozone or H2O2) then brown and finally green algae appear. This means that black algae is more likely to grow in less oxidative envionments than green algae. This is in line with what we know of black algae, that it grows under conditions of low chlorine (low oxidation potential) over an extended period of time. Another characteristic of black algae is that it has a heavy, gelatinous cell wall and it tends to grow in layers, one upon the other. Therefore, a first line of defense in killing is it frequent brushing with a wire algae bruse and using a combo wire/nylon brush for normal pool brushing (assumiong a plater pool---however black algae is not as extensive a problem in fiberglass and vinyl pools).

[smallpooldad]

Waterbear,

ORP at 700 is approximately FC of 6.

At night as the sun sets ORP might get to 725, but only if I run the pool into the night say 10 pm to 11pm if my children are having a party and I set it higher say at 775 will it ever reach 750.

The main issue I believe is that we live up at about a 1000 ft and trade winds averaging 16 to 24 mph blow very fine dirt into the pool. So 800 will never happen unless I run it 24/7 and we do not have the money for that. Trade Winds are an issue for most pools in Hawaii, I love the trade winds it keeps us cool on hot days but they do blow around a lot of dirt.

I would really like to get one of those low pressure pumps that one can run 24/7 that uses only a little electrical current but sadly they are only manufactured for 2" lines.

So FC of 6 it is. The pool is brushed daily so there is no algae of any kind present at this time that we are aware of.

Thank you for your help.

[smallpooldad]

Waterbear,

I did a little further research.

While ORP values are useful values for predicting algae breakouts in aquariums the ORP value for aquariums do not translate to pools, as marine aquariumss are controlled environments (where the temperature, UV, are constant and wind normally plays no part) albeit that higher values can guarantee higher FC chlorine levels. Predicting algae breakouts in pools using marine aquarium guidelines would normally not be of value as other levels such as ammonia, nitrates, nitrites, phosporous, and especially the fact the salt ppm (normally 30,000 to 50,000 ppm) in marine aquariums is many times greater than in a pool. Additionaly chlorine is normally not used in salt water aquariums but Nitrifying bacteria are used, this is not so in salt water pools, see here:

http://en.wikipedia.org/wiki/Aquarium

It seems that two pools with identical ORP values can have different levels of FC, and even these ORP values can fluctuate quite a bit depending on the time of day.

For example an ORP value of 700 in one pool may indicate an FC of 6, while and ORP value of 650 in another may also indicate a FC of 6. Even the same pool can have wildly swinging ORP numbers in the course of one day but still have FC readings of 6 consistently throughout the day.

Obviously as with aquariums the larger the size the less the fluctuation, a 50 gallon tank will fluctuate more than a 500 gallon tank, so it seems this is also true of pools.

I believe that in a post from Chem Geek he stated that ORP value was not as valuable to pool chemistry as once thought and that the HOCL % was a better indicator as far as algae control was concerned. At least that is the way I understood his post. And from practical experience I would have to agree.

The time line of bacterial cross infection between humans is affected by ORP but at levels of 650 or 700 depending on your view, or 750 in a public pool, this is not a concern; at least in regards to algae control. 650 ORP is the current standard for most US public pools, Germany's is 750 but that as you know is extremely hard to achieve without very sophisticated equipment, which most US public pool do not have at present.

Additionally most persons do not have ORP controllers or complicated ozone setups to mitigate the loss of chlorine so for the average person HOCL% would most probably be an easier number to strive for as it can be easily calculated using CyA, pH, and the FC numbers.

It seems therefore that for those with no algae problems a SWG pool would be optimized at pH 7.5, CyA 35, and FC of 4, this gives an approximate HOCL % of 0.050 %, which could be considered a minimum standard. For those with algae issues the FC is better kept at 6, an HOCL % of 0.080%. Obviously if one raises the CyA ppm then one would have to either lower the pH (harder on the eyes while swimming) or raise the FC which most SWG are unable to do as they struggle at FCs of 5 or 6, unless they are oversized.

Any thoughts?

[waterbear]

The only reason I brought up the algae growth in aquariums is because ORP is a good indicator of the type of algae growth and if you are getting black algae then your ORP is too low. There really is NO direct correlation between FC and ORP. It is apples and oranges. 650 MV is the minimum recommend ORP for pools with 850 mv usually the recommended high end. My point is if you ar getting black algae then your ORP is too low.
I agree with Richard that ORP is not as valuable as FC levels in predicting whether a pool will have algae outbreaks or not but for an automated system it's what we have (unless you want to spend the money on a direct reading chlorine probe and controller!)

You are in error about lowering the pH to raise the HOCL levels when there is CYA present. Once CYA is present in the water the effects of pH on HOCL/OCl- concentrations goes pretty much out the window.

If the SWG is using ORP control then you have a problem raising the FC unless the unit is oversized, However, when CYA levels are higher then there is much protection from breakdown, not only by the formation of chlorinated isocyanuates but also by physical protection of the deeper. levels of water from the CYA which does act as a 'sunscreen' in this respect so chlorine loss from sun can be minimized even more. Richard has been commenting on this in many of his posts at troublefreepool.com


In actual practice it has been found that most SWG pools without ORP controllers do best at a CYA of 70-80 ppm (or even up to 100 ppm in places like Arizona -- and possibly Hawaii), a FC of 3-5 ppm, and pH kept between 7.6-7.8 with a TA of 60-80 ppm and CH dependant on pool surface with a plaster surface around 350 ppm CH to maintain the CSI.

IMHO, ORP complicates a salt pool. While it is useful in automating a commercial pool, whose chlorine demand can fluctuate greatly throughout the day (and I know a bit about this since I do maintain 2 large commercial pools, 2 spas, and a splash zone at a resort condo), it really is overkill on a residential pool and I feel it makes maintenance much more complicated.

[smallpooldad]

Thank you for your reply.

My apologies I made an error in the last posts HOCL % should be read as HOCL ppm.

Does this mean that the calculations in the "PoolEquations" spreadsheet are incorrect?

Using the numbers you mentioned above it seems that the HOCL ppm comes out in orange as 0.021, and the CSI comes out also in orange as 0.46. Orange I believe is cautionary, in that the HOCL ppm is too low, and the CSI is too high which is potentially damaging to the plaster. Please excuse me if I am reading these numbers incorrectly.

Here are the "PoolEquations" numbers.

Measured pH 7.7
Total Alkalinity (ppm CaCO3) 60
Free Chlorine (ppm Cl2) 4.0
Cyanuric Acid (ppm CYA) 70
Calcium Hardness (ppm CaCO3) 350
Total Dissolved Solids (ppm) 3,913
Total Sulfate (ppm SO42-) 0
Total Borate (ppm Boron) 50.0
Total Ammonia (ppm Nitrogen) 0.0
U.S. Gallons 10,000
Temperature (oF) 83

Total Chloride (ppm NaCl) 3500
Carbonate Alkalinity (ppm CaCO3)25.9
Langelier Saturation Index (LSI)-0.33 (shows as red danger too high)
% HOCl (vs. Total Free Chlorine)0.5%
OCl- (as ppm Cl2) 0.042
HOCl (as ppm Cl2) 0.021 (shows as orange cautionary too low)
Calcite Saturation Level (CSL) 0.35
Calcite Saturation Index (CSI) -0.46 (shows as orange cautionary too low)

If one uses the numbers that I calculated then the numbers come out within range and show no cautionary orange but a good green:

Measured pH 7.5
Total Alkalinity (ppm CaCO3) 80
Free Chlorine (ppm Cl2) 6.0
Cyanuric Acid (ppm CYA) 35
Calcium Hardness (ppm CaCO3) 425
Total Dissolved Solids (ppm) 3,933
Total Sulfate (ppm SO42-) 0
Total Borate (ppm Boron) 50.0
Total Ammonia (ppm Nitrogen) 0.0
U.S. Gallons 10,000
Temperature (oF) 83

Total Chloride (ppm NaCl) 3501
Carbonate Alkalinity (ppm CaCO3)61.8
Langelier Saturation Index (LSI)-0.07
% HOCl (vs. Total Free Chlorine)1.3%
OCl- (as ppm Cl2) 0.100
HOCl (as ppm Cl2) 0.080
Calcite Saturation Level (CSL) 0.63
Calcite Saturation Index (CSI) -0.20

If one changes my CYA number only, which you state has no effect on the HOCL relationships, then the numbers look like this. It clearly shows a relationship. Either the spreadsheet is wrong and needs to be modified or your statment might be incorrect. I wish Richard would clear this up for us.

Here are the numbers with CyA adjusted:

Measured pH 7.5
Total Alkalinity (ppm CaCO3) 80
Free Chlorine (ppm Cl2) 6.0
Cyanuric Acid (ppm CYA) 70
Calcium Hardness (ppm CaCO3) 425
Total Dissolved Solids (ppm) 3,933
Total Sulfate (ppm SO42-) 0
Total Borate (ppm Boron) 50.0
Total Ammonia (ppm Nitrogen) 0.0
U.S. Gallons 10,000
Temperature (oF) 83

Total Chloride (ppm NaCl) 3481
Carbonate Alkalinity (ppm CaCO3)50.4
Langelier Saturation Index (LSI)-0.15
% HOCl (vs. Total Free Chlorine)0.6%
OCl- (as ppm Cl2) 0.044
HOCl (as ppm Cl2) 0.035 (reads cautionary orange i.e. too low)
Calcite Saturation Level (CSL) 0.51
Calcite Saturation Index (CSI) -0.29

Even though it seems from some real live experiences of some, but not all, members of this forum (although not proven) that the CYA protects deeper levels the FC is still too low in relation to the HOCL ppm when calculated. My pool is ranges from 4 ft to 4 1/2 ft deep so depth is not an issue for me.

I would agree as I stated above that ORP complicates the issue as it seems to me that, once set, it only stops the further production of chlorine. Although that is a benefit. And I agree, as stated in my previous post there seems little relationship between ORP and FC. "NO" relationship I am not sure I could not be that definitive as I am neither a chemist, physics major, nor biochemist.

As regards Hawaii and Arizona I think there is difference, we are very close to the ocean, in my case just 1 1/2 miles, Arizona is far. Hawaii is humid most of the time Arizona is dry most of the time, although I have been there when it was very humid. In Hawaii mold grows even on the sidewalks, in Arizona I believe this is not so. Sea going algae must be carried in by the winds here, normally 16 mph to 24 mph. It is unlikely that sea going algae blows into Arizona from the Pacific, although a little might make it.

The black algae here seems to be of a more virulent strain than that which grows in most parts of the mainland.

From my real life experience and that of my friend a FC of 4, pH of 7.6 or above, and a CyA of 70 guarantees one black algae at least where we live, especially in our old plaster pools.

At the present time I think we both beg to differ with each other. As I wrote above it would be good if chem geek could step in and discuss the spreadsheet as this seems to be the area where we disagree. It is entirely possible that it cannot allow for the effect of CyA in a salt water system. If this is so maybe a separate spreadsheet need to be written for salt water pools.

Please bear in mind my pool is 12 years old and while it has virtually no de-lamination it is old, my friends is severly de-laminated and is 17 years old.

At present I will stick with my system as it works for me in Hawaii.

It is entirely possible that we are both right, in our own ways.

One question I do have is, do you not like the pool setup numbers I use, they do not seem to be detrimental in any way? They are admittedly very cautionary.

Lastly as this is getting technical the moderator might wish to move us to the "China Shop". That would be fine by me but it is up to the moderator.