Flakes from the heater

[jpgoblue]

Help... I have a small fiberglass pool (about 4-5,000 gallons) and spa (500 gallons). Everytime I run the heater I get little white/blueish-green flakes that deposit on the bottom of the pool/spa. The flakes only appear when I run the heater, not when it's just filtering. I make sure I keep my PH around 7.4-7.8 and alkalanity around 100 or so, as I had a problem when I first got them installed and no one informed me about low levels causing corrosion. The first few weeks or so, I had very low levels of PH and Alk, which caused the light housings to corrode and the original heater to corrode as well. But that was two years ago and I have been on top of it ever since... the new heater is about nine months to a year old. It drives me crazy that they appear and makes a mess that I have to clean everytime someone wants to go in. I have no idea what is causing them or how to get rid of them and I've had a couple of guys out to look, but they were no help... any ideas? Please...

[Guest]

What manufactuer & model is your heater?

[mr_clean]

I have seen this before and it was do to the owner running the spa temp very high and using liq-chlorine. I suggested for him to use less liq-chlorine and use more chlorine tabs and check chemicals weekly. The heater was basically burning the liq-chlorine into crystal form.

[Backglass]

I have seen this before and it was do to the owner running the spa temp very high and using liq-chlorine. I suggested for him to use less liq-chlorine and use more chlorine tabs and check chemicals weekly. The heater was basically burning the liq-chlorine into crystal form.

This makes no sense. Please explain how chlorine from a liquid would somehow crystallize and "burn", yet the identical chlorine from a tablet would not?

[mr_clean]

Liq-chlorine has salt, tabs do not, as for pissin you off, I really do not care, as like you was just tryin to help someone out..............not trying to show someone up. God forbid someone else might know something.

[chem geek]

Though bleach and chlorinating liquid contain additional salt, all forms of chlorine reduce to chloride when the chlorine gets used up so salt levels build up from all sources of chlorine. They just build up twice as quickly from bleach or chlorinating liquid as from Trichlor or Dichlor (Cal-Hypo is in between as it has some additional salt, but not as much as bleach or chlorinating liquid).

Anyway, when the chlorine is added to the pool, the chlorine and salt dissolve separately so there is no basis for saying that it is the source of chlorine that directly causes the problem. Salt pools, for saltwater chlorine generators (SWG), have far higher levels of salt in the pool, for example. Salt, as in sodium chloride, will NOT form crystals at high temperatures. It is fully dissolved in the water and will stay that way until splash-out with evaporation -- the water is nowhere near saturated in sodium chloride salt.

I think the flakes may just be calcium carbonate since higher temperatures, such as found in a heater, cause calcium carbonate to precipitate if the water is over-saturated (calcium carbonate is one of those unusual substances that actually dissolves in water better at lower temperatures). So I suspect that the combination of high pH, high Calcium Hardness (CH) and/or high Total Alkalinity (TA) is to blame and these can be adjusted so should be tested. If the saturation index is high, then the extra heat (higher temperature) from the gas heater can produce scale. The good news in this particular situation is that such scale appears to be flaking off and not just sticking to the heat exchanger which is more common. So taking care of this problem will help extend the life of the heater which would otherwise become less efficient as scale built up and the heater would ultimately burn out (or shut down from internal heat sensors).

As for the experience where switching from a liquid source of chlorine (i.e. bleach or chlorinating liquid) to chlorine tabs (i.e. Trichlor) solved the problem, that was most likely due to the acidity of the Trichlor tabs so it was the lowering of pH that reduced the scaling/flaking problem. I wouldn't say this is directly related to the source of chlorine or have anything to do with its salt content -- it is an indirect effect from the resulting pH when using the different chlorine sources. The pH can be adjusted in other ways as can the Calcium Hardness and Total Alkalinity which are also factors in the over-saturation of calcium carbonate in water.

Richard

[Backglass]

Anyway, when the chlorine is added to the pool, the chlorine and salt dissolve separately so there is no basis for saying that it is the source of chlorine that directly causes the problem.

Exactly. Thanks Richard.

[mr_clean]

Ok normally I would tell a customer using Granular or tabs for a spa only:

The white chips are calcium deposits (scale which forms on the heater elements) which are knocked off when the blowers and jets are on. This problem can be prevented by empty/refill = pool/spa water and start using a sequestering agent, such as Rendezvous PROTECT PLUS or Leisure Time SPA DEFENDER, on a weekly basis to prevent calcium and can happen with all chems reading good.

But on the above that I talked about = salt: this causes corrosion and its no joke.

The story I touched on, the guys chemicals readings were all good, he had just got a 300,000 btu pentair lo nox heater for 30,000gal pool 3 months before and pool return started throwin white chips with blue/green on edges. Also heater was set at 104degrees.

You may think it's crazy but salt is corroding the heat exchange area at a fast rate alot of the warrantys state do not hookup with salt system or warranty will be voided.
Or buy our new heater for salt pools with corrosion protection.

anyway you look at it, you have corrosion

If I remember correctly his pool & spa was only 4 to 5000 gal and a gal of liq chlorine can become alot when added and has salt in it.

[chem geek]

When I said "calcium carbonate", that is the same thing as what you call "calcium deposits" or "scale". It's not pure calcium and you don't have to use a metal sequestering agent since it will only form if you have too much calcium AND carbonate together. So it is readily managed by the proper combination of pH, Total Alkalinity (TA) adjusted for CYA, and Calcium Hardness (CH). The only time you would have to use the metal sequestrant to reduce the calcium is if the fill water was very high in CH. Otherwise, adjusting pH and especially TA will prevent scale. If one targets a saturation index that is slightly corrosive (negative), then even the higher temperatures at the heater (around 30F higher at the heat exchanger surface) won't produce scale. And in a vinyl or fiberglass pool with no exposed grout with tile, one does not need extra calcium in the pool so usually scaling is not an issue unless the fill water is high in CH (as with some well water).

As for salt causing corrosion, I have an entire thread devoted to that issue here, but it's technical. Yes, higher salt levels are more corrosive to metal and this is mainly an issue in SWG pools since the salt levels are so much higher (typically around 3000 ppm) in such pools. This is one reason why many new heaters now use titanium heat exchangers instead of copper. The blue/green edges on the white chips you saw were copper carbonate (copper dissolved into ions from the heat exchanger that then precipitate out when combined with carbonate in the water) since that is blue-green (see a picture [url]http://en.wikipedia.org/wiki/Copper(II)_carbonate]here[/url] though it will turn darker towards black as it oxidizes to copper oxide as shown here).

I disagree, however, that the use of liquid chlorine (bleach or chlorinating liquid) would lead to high salt levels that quickly. As I said before, ALL chlorine sources will have 1 ppm FC convert to 0.8 ppm salt (chloride) and the liquid sources (as well as lithium hypochlorite) add an extra 0.8 ppm salt. So even if one were to add 4 ppm FC per day, that comes to a total of 4*1.6*30*6 = 1152 ppm salt over 6 months compared to half that, or 576 ppm, if using a stabilized source of chlorine -- and these numbers assume no splash-out, backwashing, or changing of water. And adding 4 ppm FC is very unusual except in a small hot tub (500 gallons). Usually in a 4-5000 gallons pool/spa, the daily chlorine consumption would be less than 4 ppm FC and there would usually be some loss from splash-out or backwash/filter-cleaning.

Anyway, I do agree with you that in pools that use a lot of chlorine, in terms of daily FC usage, that over years they can build up salt to the level of SWG pools and therefore have similar issues. And using a liquid source of chlorine gets you there twice as fast. One can rather easily check the pool's salt (chloride) level with an AquaChek test strip or a Taylor K-1766 (as shown here). Of course, one can reduce the salt levels in their pool via partial drain/refill or more frequent backwashing (for filters that backwash such as sand and some DE).

1 gallon of 12.5% chlorinating liquid in 4,000 gallons would yield 31.25 ppm FC which is higher than usual shock levels. When the chlorine then got used up, the result would be about 50 ppm higher salt levels. So even this extreme example doesn't get you to thousands of ppm salt unless this happens frequently. Again, the main rule to remember is that any chlorine increases the salt level, but the bleach and chlorinating liquid (and lithium hypochlorite) does so twice as quickly, but it's still relatively slow.

Richard

[mr_clean]

and how many pools have you gone to with this kind of problem and fixed the problem?

it's not always the chemical balance as I stated when I showed up and checked them they were good.
What you say sounds great on paper but going out to peoples houses and trying to find out how they take care of there pool and if they even understand chemical balance is always fun

what happens to the people who's heaters do not have the titanium heat exchangers instead of copper. What do you tell them?

As for reading anthing you wrote about salt problems, I don't have to as I see the problems all the time with the customers who have salt pools.

I have also researched it and have been told by pool builders about this very problem and have they agreed it happens.

also when I go to someones house and their spa is throwin white chips because they take care of it, I do explain proper chemical reading etc. but working people who do not always maintain spa chemicals correctly will need something like defender.

[chem geek]

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

[mr_clean]

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

[chem geek]

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

[mr_clean]

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.

[chem geek]

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