help with chemicals, new clueless owner

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ciccablanc
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help with chemicals, new clueless owner

Postby ciccablanc » Thu 20 Nov, 2008 11:50

HI, We recently bought a house with a pool. I've never had an inground pool before. this is a nice size pool. The water looks GREAT sparkling and clean, all i"ve been doing is cleaning the filter baskets and the filter at the pump (which is usually empty - is this normal?) and keeping the chloranator full of 3" clorine tabs. I do this daily, and brush the pool one time weekly.

I took the water sample in to a local pool place. they said my alkanility was low. told me to add 12lbs of alkanility increaser, and 2 quarts of acid. does this sound right, or are they just trying to sell me stuff?

Should i use baking soda instead of the totoal alkanility increaser? would this be cheaper.

if so where do i put this stuff? in the skimmer basket?

thank you so much for any responses.


chem geek
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Re: help with chemicals, new clueless owner

Postby chem geek » Thu 20 Nov, 2008 13:11

Congratulations on your new pool!

The filter basket at your pump will usually be fairly clean since the skimmer basket normally catches most of what is on the surface of your pool and you probably have a pool sweep that catches what falls to the bottom. The filter basket at the pump will just catch what slips through the skimmer basket and what gets sucked into the floor drain(s).

It sounds like you are using Trichlor pucks/tabs in an inline chlorinator as your source of sanitation. Continued use of Trichlor can increase the Cyanuric Acid (CYA) level over time. For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases CYA by 6 ppm. So unless you have a small pool with a short season and dilute the water regularly, say from weekly backwashing of a sand filter, then your CYA will climb. You might get through one season without a problem, but after some time you may see an unusual chlorine demand, the water turn dull, and then get green algae. There are two ways to avoid this. One is to use a weekly PolyQuat 60 algaecide or a phosphate remover, both at extra cost. The other is to switch to using unstabilized chlorine such as chlorinating liquid or 6% unscented bleach though that needs to be added daily or every other day unless you have an opaque-to-UV pool cover.

I don't know the size of your pool, but 12 pounds of alkalinity increaser and 2 quarts of Muriatic Acid in 15,000 gallons would raise the TA by 40 ppm and would lower the pH by quite a lot, from 8.0 to 7.2 if your TA started out near 100 ppm. Yes, you can use Arm & Hammer Baking Soda instead of Alkalinity Increaser -- they are identical (both are sodium bicarbonate aka sodium hydrogen carbonate). Also, Arm & Hammer Super Washing Soda (careful: NOT the detergent) is identical to pH Up (both are sodium carbonate).

You usually add most chemicals by slowly adding them in front of a return flow with the pump running -- especially for liquid chlorine and for acid. For baking soda, you can also do this or you can slowly add it to the skimmer or generally broadcast it into the pool -- it's relatively benign though adding too much too quickly can cause calcium carbonate chunks to form if the water is already near saturation (i.e. saturation index near zero or higher).

I strongly suggest you go to the Pool School at Trouble Free Pool to learn more about how to maintain your pool including the appropriate Free Chlorine (FC) level to prevent algae for a given Cyanuric Acid (CYA) level. Also, you can use The Pool Calculator for calculating dosages.

Richard
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help with chemicals, new clueless owner

Postby Guest » Fri 21 Nov, 2008 17:16

thank you so much for all the help!! i will have my husband look at your post, as some of the stuff is over my head!!

would you put the same amount of baking soda and super washing soda as recomended of the alkalidany up and down?

thanks.
chem geek
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help with chemicals, new clueless owner

Postby chem geek » Fri 21 Nov, 2008 19:12

Arm & Hammer Baking Soda is identical to Alkalinity Up so the amounts of either would be the same. Arm & Hammer Super Washing soda is identical to pH Up so the amounts of either would be the same. There is no Alkalinity Down. The way to lower Total Alkalinity (TA) is with a combination of acid addition and aeration all done at lower pH. The procedure is described here and here though it doesn't sound like you need to lower TA at this point.

I can't say whether the amounts you were told are appropriate or not. The Total Alkalinity (TA) level you need is dependent on the type of chlorine you will be using -- Trichlor pucks/tabs need a higher TA (120-140 usually, though sometimes 100-120 is OK) since the Trichlor is very acidic, but if you use chlorinating liquid or bleach then you'd have a lower TA (usually around 80).
Guest

help with chemicals, new clueless owner

Postby Guest » Sun 18 Jan, 2009 22:22

o.k. i'm back :-). my husband just said to get the stuff at the pool place this one time, till we figured it all out - and we did :-). the arm & hammer backing soda - can i use the store brand (HEB)? it reads exactly alike just the A&H sais "pure" on the title while the HEB one doesn't.
chem geek
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help with chemicals, new clueless owner

Postby chem geek » Mon 19 Jan, 2009 03:09

Yes, you can use the store brand "Alkalinity Up" as it is identical to Arm & Hammer Baking Soda.
Me...

help with chemicals, new clueless owner

Postby Me... » Mon 23 Feb, 2009 07:01

Some quick thoughts.

Alkalinity - Baking Soda is the same (food grade), but I think you might find the Bags of Alkalinity up cheaper. I usually recommend buying a case with maybe 2 x 8kg buckets at first. Then buy the 25kg bags after to refill the buckets. Proper chemistry will keep Alkalinity Up additions to a minimum, but you will probably always be using it. Unless of course your fill water is already high.

To lower Alkalinity try calculating the acid demand and then just pouring it into one area. This should help prevent dropping the pH too much. If Alk is good and you want to lower the pH, mix the acid very weakly and pour it in all around the pool. The idea is the aicd will be too weak to do much to the Alkalinity.

Erosion feeders are a great way to add pucks. I would take a stab at just keeping 1 or 2 pucks in there at a time and keep your feeder valve turned up at least 1/2. In other words, work with the amount of pucks rather that that little valve and a full load of pucks. It will help keep chlorine spiking to a minimum and therefore a more evenly balanced pool overall.

Quick thought? Mmmm ............
chem geek
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help with chemicals, new clueless owner

Postby chem geek » Mon 23 Feb, 2009 15:22

Me... wrote:To lower Alkalinity try calculating the acid demand and then just pouring it into one area. This should help prevent dropping the pH too much. If Alk is good and you want to lower the pH, mix the acid very weakly and pour it in all around the pool. The idea is the aicd will be too weak to do much to the Alkalinity.

Erosion feeders are a great way to add pucks. I would take a stab at just keeping 1 or 2 pucks in there at a time and keep your feeder valve turned up at least 1/2. In other words, work with the amount of pucks rather that that little valve and a full load of pucks. It will help keep chlorine spiking to a minimum and therefore a more evenly balanced pool overall.

Quick thought? Mmmm ............

This sounds like the "acid column" or "slug" method and was debunked here. Adding acid always lowers both the pH and the TA. The efficient way of lowering just the TA is to follow the procedure described in this post that utilizes a combination of aeration at low pH (in the overall bulk pool water) along with acid addition to keep the pH low (since aeration makes the pH rise with no change in TA). You want to drive carbon dioxide out of the pool and this is the most efficient way to do that since carbon dioxide outgasses faster at lower pH and with more air-water mixing (i.e. aeration). Pools are intentionally over-carbonated and TA is mostly a measure of that (bicarbonate).

Predicting the pH from acid addition is complicated since it is a function of the pH buffering in the pool so is dependent (mostly) on the TA (my spreadsheet here will calculate this though an approximation can be found using The Pool Calculator). However, there is a chemical rule that is useful and that is that 25-1/2 fluid ounces of Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons will lower the TA by 10 ppm. The pH will also be lowered so if it is desired to get back to the original pH, then the water should be aerated which will raise the pH with no change in TA. In this example, if the TA were 100 ppm, then the pH would drop from 7.5 to about 7.1.

You have to be careful about using Trichlor pucks. For every 10 ppm Free Chlorine (FC) they also increase Cyanuric Acid (CYA) by 6 ppm. At even a low chlorine usage of just 1 ppm FC per day, that results in increasing CYA by over 100 ppm in 6 months. Unless you have a smaller pool with regular weekly backwashing or rains with overflow, you won't get enough dilution to prevent the CYA from building up. If you don't raise the FC proportionately to have the FC be a minimum of 7.5% of the CYA level, then algae can develop (unless you are lucky with a pool low in algae nutrients, such as phosphates). If you really want to use stabilized chlorine (e.g. Trichlor or Dichlor), then you need to either raise the FC level as the CYA climbs or use a supplemental weekly algaecide (PolyQuat 60) or phosphate remover. The science behind chlorine and CYA has been known since at least 1974 as described in the paper in this link.

I experienced the problem of rising CYA in my own 16,000 gallon pool over 5 years ago. I have an opaque electric pool cover so my chlorine usage was low at around 0.7-0.8 ppm FC per day, yet starting with 30 ppm CYA I ended up with 150 ppm CYA after just 1-1/2 years of Trichlor use (7 month swim season, so around 10-11 months at this chlorine rate). The chlorine demand shot up and I couldn't keep up easily with the Trichlor pucks and my water started to turn dull -- this was a nascent algae bloom. I was using an algaecide, but only every other week, so if I had used it weekly then I could probably have gone longer. The pool store was of no help in understanding what had happened so that's when I decided to learn pool water chemistry. Now, I no longer use Trichlor pucks (I start out with a 30 ppm CYA level added either by pure CYA or some Dichlor) and only add 12.5% chlorinating liquid twice a week (remember that my pool cover is opaque, so I still have low daily FC demand of around 1 ppm even with the pool used almost every day). This costs me only $15 a month and my pH is stable as well so long as I keep my TA lower (around 80 ppm). A higher TA would have the pH rise faster due to more outgassing when the cover is off. I have crystal clear water in spite of having 2000-3000 ppb phosphates (my fill water has 300-500 ppb phosphates as a corrosion inhibitor and the pool sometimes gets blown in fertilized soil).

Richard
Me...

help with chemicals, new clueless owner

Postby Me... » Mon 23 Feb, 2009 21:33

That whole TA/pH battle is one many people find themselves fighting. I try to get it done the simplest way or explain it the simplest way, and that seems to be it.

To really see it you need to be monitoring several pools that are running controllers. Mix the acid at about 10% and you see nice pH adjustment and a fairly stable Alkalinity reading. When someone goes and turns the mix up to straight acid or at least a much stronger mix, in come the skids of Bicarb. Is it science? Apparently not but that is what you will see happen. At least here where the Alkalinity is about 20 out of the tap.

I will go read that link later when I have more time. Thanks for passing it on.
chem geek
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Re: help with chemicals, new clueless owner

Postby chem geek » Tue 24 Feb, 2009 14:37

A lot of people battle pH/TA because they do not understand that a higher TA level causes the pH to rise faster. So if you aren't using an acidic source of chlorine (e.g. Trichlor or even Dichlor which is acidic when accounting for chlorine consumption), then a higher TA does NOT stabilize the pH but actually causes it to rise faster. Having a lower TA target is the solution in this situation. This is one of the most counter-intuitive things in pool water chemistry -- that decreasing the TA leads to greater stability. The reason is that TA from carbonates has TWO effects: pH buffering and carbon dioxide outgassing. The latter effect dominates at higher TA and is a SOURCE of rising pH that the buffering cannot overcome. This chart shows the relative amount of carbon dioxide in the water vs. air in terms of what would exist at equilibrium (which is 0.0 in the chart). As can be plainly seen, pools are intentionally over-carbonated both to provide some pH buffer mostly against acidic sources and to provide carbonates for calcium carbonate saturation to protect plaster. A higher TA and a lower pH (and greater aeration) result in much faster carbon dioxide outgassing -- it's even worse than shown in the table since the rate of outgassing varies as the square of the TA (i.e. it's not linear as shown in the table).

[EDIT] If you are using an acidic source of chlorine, such as Trichlor pucks/tabs, then you want the TA to be higher, usually 120-140 ppm, since you can then take advantage of the outgassing effect to keep the pH more stable. [END-EDIT]

In controller systems adding acid, the net effect on TA will depend on the source of the otherwise rising pH. There are several possibilities I describe below and in practice they may be in combination in some pools.

Carbon Dioxide Outgassing
There is always carbon dioxide outgassing because pools are intentionally over-carbonated. The only question is a matter of degree. Using a pool cover almost eliminates this unless there is bubbled aeration (which forces air movement in spite of the cover). The outgassing of carbon dioxide makes the pH rise with no change in TA. Adding acid to compensate for the pH lowers both the pH and the TA. So the net effect in this case is a gradual lowering of the TA over time. The general solution to minimize this acid demand is to lower the TA level to reduce the amount of outgassing or to use a pool cover or to turn off aeration sources (fountains, waterfalls, etc.). If one notices that the TA is dropping at a rate close to 10 ppm for each 25.5 fluid ounces of Muriatic Acid in 10,000 gallons (with the pH constant), then carbon dioxide outgassing is the dominant source of rising pH in the pool.

Curing of Plaster
Though the rise in pH from the curing of plaster is greatest in the weeks and even months after a new or re-plastering job, the plaster can continue to cure and make the pH rise for a year or sometimes even two. When plaster cures, it adds calcium hydroxide to the pool so raises both the pH and the Calcium Hardness (CH). If one notices that the CH is rising at a rate close to 10 ppm for each 25.5 fluid ounces of Muriatic Acid in 10,000 gallons (assuming the acid rate is adjusted to maintain a stable pH), then the curing of plaster is the primary source of rising pH in the pool. In this case, there is no change in Total Alkalinity (TA), so both pH and TA remain stable.

Chlorine Outgassing
Normally, chlorine does not outgas from the pool to a very large extent (it's more of an issue in hot tubs due to the higher water temperatures). However, saltwater chlorine generator (SWG) systems generate chlorine gas and if such gas does not fully dissolve into the pool water and instead outgasses, then this leads to a significant pH rise. SWG systems also aerate the water with hydrogen gas bubbles and this disturbance of the water surface can increase the carbon dioxide outgassing as well. For this discussion, let's assume that the TA is very low so that there is minimal carbon dioxide outgassing and let's focus on what happens if chlorine gas outgasses. Using the same example from earlier where we are adding 25.5 fluid ounces of Muriatic Acid in 10,000 gallons, then if 7 ppm Free Chlorine (FC) is (cumulatively over time) generated and outgassed as chlorine gas, then both the pH and TA will remain stable. The actual chlorine generated will be higher since some does dissolve and is used in the pool.

Water Dilution
Pool water can be diluted by splash-out, backwashing, rain with overflow, or intentional partial drain/refill. The effect on pool water chemistry is to make the pool water parameters move towards that of the fill water. So if the fill water is low in CH compared to the pool, then the CH will drop. If the fill water is high in TA compared to the pool, then the TA will rise. The effect on pH is usually fairly small, though it has more effect if the fill water is more buffered (that is, has a higher TA).

Evaporation and Refill
When pool water evaporates, all of the chemicals in the pool become more concentrated so when the water level rises from refill, whatever chemicals that are in the fill water get added to the pool. So if there are no other effects, the TA and CH will rise from evaporation and refill. This map shows the annual evaporation rate in inches for the continental U.S. If the average pool depth is 4-1/2 feet, then that's 54 inches so evaporation of 54 inches of pool water is equivalent to adding the TA and CH measured in the fill water to the values already in the pool.

Assuming one adds acid to keep the pH constant, the following are the net effects for each of the above:

............................................. TA .. CH
Carbon Dioxide Outgassing ... - .... 0
Curing of Plaster ................... 0 .... +
Chlorine Outgassing ............. 0 .... 0
Water Dilution ....................... ? ..... ? (depends on fill water)
Evaporation and Refill ........... + .... +

Richard

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