Heater Failures

[apoollover]

I found your website online, and was really intrigued someone was talking pool sense, so thanks.

I have had an in-ground concrete/plaster pool for about 6 years now. It is about 34,000 gallons and located in the Denver area. The original design included a Jandy salt generator. I have gone thru probably 10 sets of heaters/heat exchangers in this time period, but no one can seem to pinpoint the problem. I keep my water pretty well balanced, at least to manufacturer specs, and don't have any issues with crappy fill water (i.e. high alkalinity). When tested (supposedly) for electric current, the water showed only a very, very minimal current.

Last year, we switched heaters from Pentair to Raypak, and still have problems. I finally gave up on the salt system, and started using dichlor, and have still experienced exchanger failure/leaking. We just pulled out the heat exchangers from the 2 heaters, and they did not show signs of any bad water chemistry, but still had holes or cracks in the exchanger tube(s).

Do you have any ideas what might be causing this?

Also, interestingly, I never had any issues with algae while on the salt system, but this year I have battled wall stain algae. I'm not getting why the same level of dichlor chlorine can't seem to fight off the algae like the SWG? In your opinion, what is the best way to shock the water now, and to what level, and using what product?

Thanks for your time and help.


Test kit is a Taylor K2005 (used the same style for 6 years). Test results:

Chlorine: 1.5 (almost consistently kept between 1 and 2)

pH: 7.5 (we added an acid feeder last year, and it reads 7.6; the pH has always wanted to run higher with this pool. I have never stopped adding acid just to see how high it wanted to go, but the highest I ever read was a little over 8)

TA: 85 (alkalinity is always between 80-100; I would have to add alk. up to get it higher; it usually wants to go lower, but typically remains fairly stable at 80)

Calcium: 220 (calcium wants to go lower, but only once have I read it below 150; I add calcium flakes probably 2-3 times year)

CYA: 20 (haven't added stabilizer for about a month now)

I test my water at least every other day for chlorine and pH, once a week for alkalinity, and once every 2-3 weeks for calcium). I use chemical-company chemicals, not store-bought.

The original install did not have an anode, but we added one last year. It has not degraded much since last year. The circulating pump is a 3 HP, we have 2-400K btu heaters, and we have the largest Pentair CnC+ cartridge filter tank. The pool is free-form, so we do not have a robotic cleaner. It is about 100 feet or so from the pool equipment to the pool. We run the circ pump 24/7. 2" lines between all the equipment. Hopefully, that covers most everything.

Ideas?

[PoolDoc]

Do you have a bypass on the heaters? If not, the failures may well be due to high velocity erosive flow from your 3HP motor. I'd have to see the piping layout (photos!!) to confirm that.

(Why do you have a 3HP pump on a 33,000 gallon pool?)

Also, make sure your acid feed is downstream of the heater. However, since you only added it last year, it is probably not the cause.

Shock with plain 6% household bleach -- it has the fewest side effects. If you have pool bleach AKA liquid chlorine in your area, it may require less handling. However, the pool bleach stocked in this area and wholesaled by SCP is stored for long periods at high temps, so it's probably degraded to household bleach by the time users get it. Store bleach is much more likely to be at the stated %.

[apoollover]

The equipment room is pretty torn up right now since the heaters are disassembled, but I'll see if I can clean it up enough to take pics. There are bypasses on both heaters. Not sure why the reason for 3hp (original design by pool builder), but the current boiler tech thinks even that may not be enough (?). He's going to check the flow once he reassembles the heaters. Acid feed is downstream of heaters, and they installed a backflow preventer last year as well to prevent backflow from the SWG.

The pool includes a high-flow water feature using two 7.5hp pumps. But, that is on its own closed loop - it does not flow through the pool equipment directly. It is not on all the time. The pool is surrounded by granite rocks (on rock shelves), and the rocks do slough off fine, shiny, almost gold-flake-like material. I've always wondered if the cartridge filters are able to handle the material. The pool builder had told us not to change out the filters more than once every couple of years, so not sure about that.

This thing has been frustrating because everyone points their finger at chemistry, but I guarantee that the chemistry is never out of balance. The raw water does not have problems, and we pay close attention to the balance. So, it has to be something more obscure.

Thanks for the bleach suggestion. How does it register, then? High chlorine level? How much to use?

[aylad]

How does it register, then? High chlorine level? How much to use?

In 33000 gallons, each gallon of 6% bleach you use will raise your FC by 1.8 ppm. With a CYA of 20, you need to raise your chlorine to 12 ppm to achieve "shock" level. You can see the link to the "best guess chart" in Pooldoc's sig for more on the CYA to chlorine relationship.

Janet

[PoolDoc]

When you take pics, it would be VERY informative to have detailed and careful photos of both the INTERIOR and the exterior of the heat exchangers.

Ben

[CarlD]

Hi, APL:

Your assurances of "balance" raise some questions for me.
If the numbers you are citing now are the same ones you had when you were using your SWCG, then that may be one of the sources of your problems.
Ben's knowledge of pump HP and flow rates is far beyond mine so I'm just going to look at the chemistry. It may well be you are simply blasting too much water through your heaters and that is the cause of failure. I don't know.

Back to the chems.
FC: 1.5
CYA: 20
TA: 85

I'm not the SWCG expert but I do know that every manufacturer recommends a relatively CYA level of something like 70-90ppm
At those levels, FC should be no less than 5% (so CYA=80, FC >= 4ppm).
Also, a rising pH can mean your TA is too high. For years we were taught TA should be 90-120, with some scales going from 80-125. But we've been finding out experientially that this is not necessarily true. For example: All this season my TA has been a startlingly low level of 60-70ppm. WELL below "standard". Yet my pH has been MORE stable this season than it ever has been. What seems to be the REAL case is that pools with rising pH tend to be "happier" with lower TA levels. In fact, for SWCG pools, our resident experts ALWAYS recommend lower TA levels. Still, also it's well-known that many SWCG owners face continual rising pH.

What also concerns me (and I may WELL be off-track here) is that your continual acid feed may not dilute properly by the time it reaches the heater...if so, the problem is pretty straight forward. Have you ever considered testing water (somehow) just before it enters the heater to see if its pH is low?

So, I'm guessing you have a number of potential causes of your regular heater failure.

These are just some thoughts.

Carl

[apoollover]

Hi Carl,

Thanks for the reply, and great feedback. So, what are we supposed to do? The heater manufacturers all give you the levels they want you to have, and NONE of them tell you to have a FC level above 3. Yet, they do recommend CYA at, I believe, 70. And, going off Ben's guide, a CYA of 70 equates to an FC level of between 5 and 10. If a manufacturer saw that you had those levels, they would immediately point to the water being too corrosive. Plus, and I'd have to go look at the "wheel", but I think that would create other problems when looking at Taylor's water balance wheel?

My pH has continued to rise even after I stopped using the SWG, to my surprise. Not really sure why that would be. Regarding your concern of the acid feeder, I have to dilute the acid in the tank anyway so that the pool pH stays consistent. Plus, it feeds just outside of the filter tank on the return to the pool, so the higher acid level in the tank gets diluted before it returns to the heaters (i.e. only pool water hits the heaters). Plus, we had a majority of our heater failures before we put the acid feeder in. I only put the acid feeder in for convenience and to try to maintain a more consistent pH, rather than adding multiple cups every day or two.

So, maybe, from your feedback, the question is: by following the manufacturer recommended chemistry levels, am I actually creating the problem? I'm not a chemist, but intuitively, it seems to me like having higher FC, lower TA, and higher CYA would make the water more corrosive to heaters?

Ben, I'll try and get photos of the heat exchangers when the tech brings them back. He was going to call Raypak to talk to them, and then ship them back using the boxes from the new exchangers, which are at my house....

By the way, Ben, for flow-purposes, I have 3 skimmers, and two main-drains. The pool is only 6.5 feet at its deepest (not sure if that makes any difference).