Flakes from the heater

Total hardness and calcium hardness in pool water.
Scale, calcium buildup, hard water and scaling problems.
chem geek
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Postby chem geek » Sat 18 Aug, 2007 15:59

mr_clean wrote:it's not always the chemical balance as I stated when I showed up and checked them they were good.

Many people say their chemicals are "in balance" when they are not. Did you calculate the Calcite (Langelier) Saturation Index? If all the parameters of pH, TA and CH are at the high end of their "recommended" ranges, then the result is scaling at higher temperatures -- namely at the heater. Also, scale takes a while to build up so the chemistry could have been out of balance for a while before you showed up, and then the pH went lower and the scale already formed in the heater started to flake off. Many of the saturation index pool calculators are wrong. The best one is the Taylor Watergram found in some Taylor combination kits (such as the K-2005 and K-2006), but you can also use the online calculator here that Jason developed based on my spreadsheet (and matches the Taylor watergram). By the way, when such a saturation index is negative and says it's "corrosive", that is inaccurate -- it's corrosive only in the sense that it will tend to dissolve plaster or grout (specifically calcium carbonate), not necessarily metal. Metal corrosion has other factors including oxidizer level (chlorine and dissolved oxygen), pH and salt level (conductivity, mostly, though chlorides are additionally corrosive to stainless steel by interfering with the healing process of forming a protective layer as I described in the link you didn't read because you apparently know all about this already).

For people with copper heat exchangers, I would recommend they think twice about getting an SWG system or get a new gas heater (with titanium heat exchanger) since there is no way around the corrosion problems at the higher salt levels of SWG pools (3000 ppm salt). They could run their pools at very high pH to minimize the problem (and keep TA and CH lower to compensate to prevent scaling) but this will be harsher on the eyes. And they can keep the lowest chlorine levels possible by using supplemental algaecide (PolyQuat 60 weekly) as that will also help. But really, if you are getting an SWG, then you most likely need to get a gas heater made to tolerate the higher salt levels. People used to use stainless steel filters until those also had problems at higher salt levels -- now they are almost all plastic (of course, cost was part of the reason for the change as well). I should point out, however, that most damage to copper heat exchangers is from improperly maintaining the pool, SWG or not -- namely, putting Trichlor pucks in the skimmer with the pump not always on, for example, or just using Trichlor as the source of chlorine and not monitoring the pH (and TA) of the pool (so it becomes more acidic which then corrodes the copper, even in low-salt pools).

As for needing Defender or other metal sequestrants to reduce calcium levels, even those people who do not properly maintain their pools won't need that since the only way to get too high a TA or CH is to add those chemicals (Alkalinity Up / Baking Soda and Calcium Chloride) to the pool so a lack of maintenance could only lead to scale if they let the pH go way up. As I mentioned before, the exception to this is if their fill water is already high in CH and/or TA (e.g. well water) in which case I would agree that a calcium sequestrant or filtering through a water softener are reasonable options. If the pool does not have a lot of dilution through splash-out or backwash, then in areas with very high evaporation the fill water will add to the CH and TA so that's another way the CH can build up, but just recommending Defender as a blanket solution is adding a band-aid to the problem without locating its source -- where is the higher CH coming from -- is it from not understanding the saturation index so adding too much initially? Or is it from fill water initially high in CH? Or is it from high evaporation and low dilution and fill water with moderate CH? Most pools do not have high CH unless you are operating in a region where the fill water is high in CH (which you can test, of course, or look at the water quality report, though they often just report Total Hardness and not necessarily Calcium Hardness).

Anyway, you seem to have a good handle on all pool problems so I'll let you take it from here for this forum. Though I value the experience you provide and information you share, I'll stay over on TroubleFreePool(dot)com and the original PoolForum(dot)com instead. You obviously feel I have nothing to contribute.

Richard


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Postby mr_clean » Sat 18 Aug, 2007 16:40

Chem geek, I understand what you are sayin and I am not trying to tell you, your wrong. You are correct that pool could have been out of whack for months/years and was just brought back to life.

but with dealing with all kinds of customers I go by what they tell me and go from there. If they are lieing to me, it's only hurting them.

Also not tryin to make you leave, feel bad or anything else, just explaining a situation that has happened.

I do think you explain things correct but sometimes feed them to much info.

plain and simple - was just tryin to help someone

The guy who trained me years ago always said- keep it simple stupid
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Postby chem geek » Sat 18 Aug, 2007 17:28

Some people on these forums just want a quick answer to their current problem. Others want to know why the problems occurred so they can prevent them from happening in the future. Still others want to know details so they can contribute additional solutions with more information. So it really varies and anyone that doesn't want the detail can skip over it.

Because there is so much speculation, misinformation, and even lies in this industry, I am very, very sensitive to making sure that information is technically correct. That is distinct from the experiences themselves -- that is, it's not about questioning what is seen, but the "why" explanations.

Just one example is where everyone in the pool industry believed that the significant rise in pH nearly all SWG pools was due to the production of chlorine from the SWG being alkaline/basic (i.e. high in pH) and they even described the chemistry in the salt cell to prove it. This was a flawed analysis since they didn't take into account the usage of chlorine (via breakdown from sunlight, oxidation of organics, or disinfection of pathogens) and when I looked at the whole picture I found that the SWG is pH neutral, just as bleach or chlorinating liquid or Cal-Hypo are all (nearly) pH neutral -- again, something that the industry doesn't say, but is proven in pools where aeration is minimal (including those with pool covers).

I then figured out, along with information and experiments from others on forums, that it was the increased outgassing of carbon dioxide from the pool due to the aeration from the hydrogen gas bubbles produced from the SWG that was causing the pH to rise so one solution to this rising pH problem was to lower the TA (to 70-80 in high CYA pools and even to 50-60 in lower CYA pools) and this solved or significantly reduced the rising pH problem for almost every pool where it was tried. The lowering of TA to actually stabilize pH is the most counterintuitive thing in pool water chemistry though it makes perfect sense when one looks at the full chemistry and physics of what goes on in pools, all of which are intentionally "over-carbonated".

So experience is critically important, but understanding the science behind pool and spa chemistry is also important and leads to real solutions that would not otherwise be found -- after all, SWGs have been around for quite a while and yet no one (at least no one reporting on any pool forums) stumbled upon using a lower TA to solve the rising pH problem.

So let's work together with your experience and my science knowledge to figure out and solve more problems.

Richard
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Postby mr_clean » Sat 18 Aug, 2007 17:50

Just a note I was told PH rises do to high TDS from the salt.

How low are you saying the TA should be?

We know salt already corrodes and to low of TA corrode metal etc.

I would not own a swp myself.
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Postby chem geek » Sat 18 Aug, 2007 18:57

mr_clean wrote:Just a note I was told PH rises do to high TDS from the salt.

How low are you saying the TA should be?

We know salt already corrodes and to low of TA corrode metal etc.

I would not own a swp myself.

Unfortunately, what you were told about TDS and pH is incorrect. The pH does not rise due to the high TDS, which is mostly salt. There are people with high salt level pools where they either aren't using their SWG anymore or just wanted the feel of higher salt (the latter group are usually at around 1000-1500 ppm, not 3000 ppm) and they don't experience the high pH rise as much as SWG users.

Next time you can be at a pool with an SWG, go there at night and turn on the SWG (and pump, obviously) and turn on the interior pool lights. You'll see the many tiny hydrogen gas bubbles coming out from the returns. When the SWG is on, the pool is being quite vigorously aerated and that drives the extra carbon dioxide that is in the pool out into the air. For technical reasons I won't get into here, that causes the pH to rise with no change in TA. When you later add acid to get the pH back to normal, this lowers both the pH and the TA so the net effect long-term (in addition to annoying pH rise and acid addition) is a lowering in TA.

In fact, the principles of carbon dioxide outgassing are used to be able to lower the TA as I describe in this post. Lower pH and higher TA cause faster outgassing as does more aeration. Faster outgassing means faster pH rise and more acid needed to restore the pH. Think of a pool as a carbonated beverage, which is actually technically accurate except that it isn't as carbonated -- the initial carbonation comes from the addition of Alkalinity Up or Baking Soda or is already present in the fill water (essentially, the carbonate portion of TA). Think of what happens when you blow bubbles through a straw or stir up the drink to aerate it -- the drink goes flat faster because it loses its carbonation by outgassing carbon dioxide into the air. If you were to measure the pH of the carbonated drink, you would find that it was highly acidic initially (as low as 2.5 in pH) but that after blowing bubbles and having it go flat the pH goes up. As for accelerating the outgassing by lowering the pH, think of adding vinegar to baking soda or to a solution of water with baking soda added to it. Vinegar is acidic (it's acetic acid) and you will see carbon dioxide bubble out of solution. In a pool, the carbonation isn't high enough to have bubbles form in the water even when Muriatic Acid is added, but lower pH nevertheless does increase the rate of outgassing.

There isn't a single answer for how low the TA should be because it depends upon the amount of aeration for that pool and some pools have waterfalls, spillovers, fountains, etc. that even without an SWG would cause the pH to rise quite a bit. If a very low TA is used, however, a plaster pool needs a higher pH or CH (or both) to maintain proper water balance (calcium carbonate saturation) so if the TDS is 3200 (due to salt being 3000) and the CYA is 80 and the TA is 80, then the CH can be 400-500 at a pH of 7.5 or the pH target can be 7.7 with a CH of 300. In a non-salt pool with a TDS of 1000, then a CYA of 30, a TA of 70, and a CH of 400 is good for a pH around 7.5 to 7.6. So it all depends on how things settle down so adjusting the TA and then the pH to find the long-term sweet spot is the first thing to do and then adjust CH as needed. Targeting a saturation index of around -0.2 or -0.3 should prevent scaling at the heater. I think the lowest TA any SWG user with high CYA has done is 70 and the lowest any non-SWG user with low CYA has done is 50 (but this needs a much higher CH and/or pH target if the pool is plaster -- for vinyl pools, it's not a problem).

The low TA doesn't corrode metal. As I said before, the "corrosion" from a negative saturation index, which can be from low pH, low TA or low CH (or lower temperature or higher TDS) has to do with dissolving plaster (calcium carbonate), not metal. There used to be a theory that said that having calcium carbonate saturation would protect metal from corrosion, but that's been pretty much discounted as it's nearly impossible to create the proper thin layer to protect from corrosion without building up too much scale or having an uneven surface. Instead, metal corrosion is much more a function of the oxidizer level, the pH (lower is worse), and conductivity (higher TDS, including salt, being more conductive). Low TA means lower carbonates in the water and that is the least important factor in metal corrosion.

I should also point out that there are other methods that can be used by themselves or in conjunction with the lower TA to reduce the effect of increasing pH in an SWG pool. These other methods all seek to lower the SWG output which thereby lowers the hydrogen gas bubble production, the aeration, and the outgassing of carbon dioxide. One of these methods is to use a higher CYA level, usually around 60-80 ppm. Though normally this is something to be careful of since it's so hard to fight algae blooms when the CYA is high, in an SWG pool it's usually OK since there is some superchlorination in the SWG cell and the chlorine level in the pool tends to be more consistent. The higher CYA level protects the chlorine more from sunlight so the SWG output can be turned down and this is even true when the FC level is raised to compensate for the higher CYA level (though typically people run an SWG pool at around an FC level of 4.5% of the CYA level so CYA 60-80 has FC of 2.7 to 3.6 ppm).

Another method to reduce SWG output and therefore the pH rise associated with aeration and outgassing is to add 50 ppm Borates to the pool (this is what Proteam Supreme does, for example). The Borates are an algaecide and help inhibit algae growth so that chlorine doesn't have to. Another pool user and active forum participant, waterbear (Evan) figured out the Borates and described this in this thread .

Many people are happy with the convenience of SWG, but there are issues with corrosion depending on the pool materials that are used. Some areas of the country experience much heavier corrosion, such as Texas and Arizona, due to the types of stone materials that are used (often limestone, though also flagstone) and the high evaporation rates and relatively low amounts of summer rain (compared to Florida, for example). Early in the first post that I linked to regarding corrosion in SWG pools goes to a blog where there are more reports of corrosion, but most SWG pool users on multiple pool forums aren't reporting this so it's a bit hit and miss. Clearly, higher salt levels are more corrosive, but how much so depends on the materials used for hardscapes (stone), heaters, and the type of stainless steel that is used. The absolute worst cases for metal corrosion in SWG pools are those used indoors when CYA is not used since the disinfecting chlorine level is so much higher -- the simple solution would just be to use CYA in such pools (and in fact I believe CYA should be used in all indoor pools, but I won't get into that now).

Richard
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HIGH PH IN SWG

Postby hardypoolman » Thu 23 Aug, 2007 20:16

Work on 95 SWG pools here in Florida. Our average CH is between 250 and 280 ppm. Our units that we use, Aqua Rite and Aqua Logic states that TA should be between 80 and 100. If you want to see what the gassing situation is then make up a 5 gallon bucket of salt water with a reading of 3000 ppm. Set the cell in the bucket. Now you will need to put another old cell in place of the good one or a made up pipe with the unions on it so water can flow through it since the Aqua Rite is tied into the pump and gets its power when the pump is on. Turn the unit on either to 100 percent or superchlorinate. Once that is done turn the system on and watch the bubbles flow out of the cell. It will show you how strong the gassing process is.

To make a long story short, lower TA does help some in lower PH levels and aids in the calcium buildup. Proper cleaning of the tiles, by using a half acid and half tile soap mixture will help greatly with regular maintenance. It takes a while to build up and takes awhile to remove. The key here is proper maintenance.

Be careful with the products used. CLR works great on calcium but destroys marble. If someone has the ultimate product for removing the calcium formations, let me know. Also muriatic acid works great but you maust use care to rinse it and all products off well.

We have had some luck by putting Metal Magic in a spray bottle and spraying the tile and just leaving it to work. Grout damage was none.
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Postby fatybabe » Wed 29 Aug, 2007 21:36

I would suspect that beside the usual calcium corrosion is also happening at the same time. Usually you will tend to find heaters made of copper or a copper based alloy.

The corrosion would probably tend to be because of your heater temp, h20 becomes more active and the usual practice with big boiling systems is to include some oxygen scavangers.

Maybe you should try some stuff like COP OUT to control that although ultimately it doesnt prevent the corrosion however what it does do is prevent the staining from happening.

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