Endless Pool with High Alkalinity

[Jeffm]

I installed an Endless Pool this year.
It's 8'x14' and about 3.5' deep, so about 3,000 gal.

The perimeter has stainless panels. (This means if you drop the pH too much, you'll have corrosion problems.)


I've got really high Alkalinity issues. It just tested at 400ppm. Having trouble dropping it without dropping pH too much (should really stay above 7.3)

My fill water was from my well. Roughly 300ppm Alk, and Ca hardness.

Once I filled the pool I got the Alk down to 200, and waited a bit to take it down some more. As the pH increased I added Muratic acid as I could, and didn't really test Alk for a while. I just tested it (and got it verified by a local pool supply) and I'm up to 400 ppm. That's right...Alk has gone up.

I use chlorine tablets, because they have an acid content. I've added some anti-algae stuff, and a little soda ash.

I have no idea why my alkalinity is going up, and really need a good reccomendation for lowering it without dropping my pH too much.

[chem geek]

Unless you have some sort of testing problem, the Total Alkalinity (TA) may be going up if you have lots of evaporation of water. The fill water will then add to the TA. However, with the frequent churning of the water from the Endless pool, this should give a decent amount of aeration and with your use of an acidic source of chlorine, it does seem strange that the TA would go up.

First check the rate of evaporation as well as check for any leaks by seeing how quickly a bucket of pool water drops relative to the pool water level (turn off the fill water source to the pool before making this test). If you have a leak (the pool level drops faster than the bucket level) or a lot of evaporation (3/4") then that might explain it. Even with 1/2" evaporation per day, one week would be 3.5" out of the 42" depth so would add (3.5/42)*300 = 25 ppm TA per week (so 300 ppm over 3 months). That doesn't sound fast enough to what you are seeing unless this was over several months and that your pool didn't get a lot of aeration (which would be strange).

Richard

[Jeffm]

There is almost no water loss.

The pool is located indoor (sunroom). When it is not in use I keep a security cover on it. The room isn't even humid when you walk inside.

Any water loss occurs from splashing. I did a drain/fill about 80 days ago. The water level has dropped about 1/4". I haven't added any water since the fill. The only additions have been a few gallons of Mur Acid, and some Soda Ash mixed with water.

There is no leak, the pool is half in ground half above, with a tile deck around it. (about 18" high) (Epoxy Grout), I have access panels in the deck and have been working in there frequently, any leaking would be visible as damp concrete.

I'm guessing you're going to reccommend your method of lowering Alk first?
Would still like to know why it's rising. It didn't get alot of use for the first 30 days....but we're using it about 1 hour every other day for the past 30.

I didn't believe my own Alk readings, so I've been getting it confirmed by a local pool supply.

[mr_clean]

what is your CYA/conditioner reading at? High conditioner levels will make alkalinity levels look higher when testing.
If CYA is say 100 and TA reads 200 your real TA level would be 170. You basically divide by 3 what ever CYA is and subtract from TA. Sense you use tabs which have CYA in them you could be getting higher readings.
Also when adding Soda-Ash to raise PH, will also raise TA.
Chem Geek has a post on aeration which helps lower TA and keep PH level up.


Try aeration

[chem geek]

The TA lowering procedure is here, but I agree with you that it would be good to figure out the source of TA rise and you've pretty much eliminated all the other factors that could make that happen.

Though it is true that CYA is one component of TA, at a pH of 7.5 only one-third of the CYA ppm is the amount it contributes to TA so that may not be enough to explain what you are seeing unless your CYA is through the roof (which it might be if you have been only using Trichlor pucks/tabs). On the other hand, technically speaking when you add Trichlor, it lowers pH at the same time it increases CYA and the net effect of this is no change in TA. If you were to raise the pH by adding a base, then the TA would go up along with the pH.

So, have you ever added any pH Up product? If so, then this is the source of your TA increase along with the use of Trichlor pucks/tabs. pH Up is Sodium Carbonate (aka Soda Ash as mr_clean said) and not only increases the pH, but also adds carbonates which increase TA. That would explain the situation though normally carbon dioxide would outgas from the pool to make the pH rise and then the acid from the Trichlor would lower the pH and TA -- usually this balances out well below the TA level you are seeing and you wouldn't need to add any pH Up product. Perhaps being indoors in an enclosed environment, there is more carbon dioxide in the air or there is less outgassing for whatever reason.

For example, in 3000 gallons, one 3" Trichlor puck ( that weighs 8 ounces; some weigh 6 or 7, but I'll assume 8 ) and accounting for chlorine usage (which is also an acidic process) will require 13.4 ounces weight (about one and a half cups) of pH Up to maintain the pH assuming no outgassing. This combination causes the TA to rise by 18.6 ppm. So after 10 such pucks, one could increase the TA by almost 200 ppm. The one Trichlor puck/tab would add 18.3 ppm to FC and 11.1 ppm to CYA so with the pool indoors and not exposed to sunlight (or at least the sun filtered through glass to limit the UV rays), then I wouldn't expect you to go through that many tablets very often.

Richard

[mr_clean]

The only additions have been a few gallons of Mur Acid, and some Soda Ash mixed with water.

I think Soda Ash is it, & with chlorine tabs a lot of people will just go out to pool and add as many tabs as possible that will fit in floater and walk away until the next week or so.

[Jeffm]

I added quite a bit of soda ash in the past when I was trying to decrease my alkalinity. When I first filled the pool...and after it heated I was doing a balancing act with Mur Acid and Soda Ash. It was a two steps forward and one step back process, but the alk did drop. Once I got the Alk down to 200ish, I stopped using Soda Ash completely. That was about 6-8 weeks ago. Since then as the pH has slowly crept up I've added a little Mur here and there. I've only been monitoring the pH and Cl levels during that time thinking "Well the Alk , CaH etc levels aren't going to change much on their own". I figured I was due to check the Alk and after seeing the 400ppm ...well here I am.


So what you're saying is the use of Soda Ash in the past is still causing the Alk to rise?

(I'm picking up some pvc today to make an aerator btw)

I measured the CYA last night and it's 50-55ppm, so I think it's right where it should be.

As for Chlorine. What would you recommend? I use the small tablets, and I do take readings 2-3 times/week. (Not sure the size but they are about 3/4" to 1" thick and about 1.5" dia) Normally if I put 2 tablets in the skimmer on Wednesday and 2 more on Sunday my Cl levels stay around 0.5 to 2.0 I use one of those Neptune Sanitizers, which recommends a level of .5 to 1.0.

Endless Pools recommends just Chlorine Bleach, but that has a alkanine component to it, so I'm staying away from that.

[chem geek]

So what you're saying is the use of Soda Ash in the past is still causing the Alk to rise?

(I'm picking up some pvc today to make an aerator btw)

I measured the CYA last night and it's 50-55ppm, so I think it's right where it should be.

As for Chlorine. What would you recommend? I use the small tablets, and I do take readings 2-3 times/week. (Not sure the size but they are about 3/4" to 1" thick and about 1.5" dia) Normally if I put 2 tablets in the skimmer on Wednesday and 2 more on Sunday my Cl levels stay around 0.5 to 2.0 I use one of those Neptune Sanitizers, which recommends a level of .5 to 1.0.

Endless Pools recommends just Chlorine Bleach, but that has a alkanine component to it, so I'm staying away from that.

Yes, the Soda Ash causes the Total Alkalinity (TA) to rise. You want to follow the procedure I linked to in order to reduce TA. You NEVER add Soda Ash when wanting to lower TA -- you only add Muriatic Acid (or any other acid) and aerate (the aeration causes the pH to rise with no change in TA). You want to make sure not to go below 7.0 in the TA lowering procedure since you've got stainless steel sides so if your pH test kit only goes down to 7.0, then use 7.2 as a target instead for safety. A good aerator will make up for not having the pH quite as low -- it sounds like you'll be making a GREAT one! Take a look at this link for some inspiration.

At a CYA of 50-55 ppm, you will need to keep an absolute minimum Free Chlorine (FC) level of 4 ppm though should probably target 6 ppm to be safe. If you use the tablets, your CYA will continue to rise since with every 1 ppm FC added by the tablets, you will also get a 0.6 ppm increase in CYA. Unless you dilute the water via splash-out or backwash, the CYA will rise.

Your chlorine level is too low for the CYA level you have. If you want to continue to do that, then you must use an algaecide, such as PolyQuat 60, in order to prevent algae.

You SHOULD be using unscented chlorine bleach instead of the tablets. Only use the Trichlor tabs when the CYA needs to be increased. It is NOT true that bleach causes the pH to rise. Yes, bleach is alkaline (basic), BUT the consumption of chlorine is acidic and these cancel each other out. So adding bleach has the pH go up and then when that chlorine gets used up the pH comes back down again (and the swing is small). I use only chlorinating liquid (a strong form of chlorine, but otherwise identical to bleach) and have stable pH and TA. The cause for rising pH in pools that use bleach, chlorinating liquid, Cal-Hypo, Lithium hypochlorite or a saltwater chlorine generator (SWG) is the outgassing of carbon dioxide, not the chlorine itself. This happens more at higher TA and lower pH so the easiest thing to do is to lower the TA to reduce the tendency of the pH to rise. Aeration also speeds up the process, so that's why an SWG pool has a strong tendency for the pH to rise, due to the hydrogen gas bubbles the SWG produces that strongly aerate the water. Pools are intentionally over-carbonated -- that's what the high TA level is -- similar to a carbonated beverage. Just as blowing bubbles in a carbonated beverage makes it go flat, aerating pool water drives the carbon dioxide out and this causes the pH to rise (with no change in TA for technical reasons I won't get into here).

In your pool with its "endless" water movement capability, there might be higher than usual aeration so you may need to use a lower TA than normal, down to around 50 ppm if necessary. If you go that low, then if the pool is a plaster pool or has exposed grout, then you will need to use a higher Calcium Hardness (CH) level of around 400-500 ppm or target a higher pH of around 7.6-7.7. It sounded like the sides are stainless steel, but I don't know if it also has tile with grout -- if not, then you don't need to worry about the calcium level.

Do you have a link to the Neptune Sanitizer you are using? It sounds like it might be a metals (minerals) product, possibly copper or silver, and that has its own set of problems where it can cause staining at higher pH. It is also unnecessary -- chlorine alone will sanitize the pool and if maintained properly it will be at a low level. If you want to use a lower level of chlorine, then as I mentioned an algaecide such as a weekly maintenance dose of PolyQuat 60 will let you do that. Using copper for algae prevention will work, but the side effects of staining are a pain and its hard to control the copper concentration in the water to prevent that. The silver for bacteria control is unnecessary as even very small amounts of chlorine will kill bacteria very quickly -- much faster than the silver.

Is your pool outside exposed to the sun? Or is it indoors?

Richard

[Jeffm]

I could email a picture of the pool if you'd like. My email is jtmal24 at hotmail

The pool is located indoors, in an all glass sunroom. High R values on the glass, it does get warm at times. When not in use the pool is completely covered with an opaque vinyl, tracked security cover. This really seals up the pool completely.

The "wet" part of the pool is a full vinyl-rubber liner, with a 316 stainless bench around the perimeter. Also the propeller until is stainless and some other corrosion resistant materials. (Although I do have some rust formation that I'm not happy about, probably from when I first filled the pool and got the pH too low)

Above the waterline...there is 2" of porcelain tile, before you get to the horizontal porcelain (ceramic) tile deck. So..the tile is not submerged but does get splashed and condensate. The grout epoxy, just like an epoxy floor basically. Gotta use that in wet environments.

I'll have to look for a link on the neptune system. It does have metals...copper and silver. Oops It's Nature2 not neptune.
Just Google Nature2 and pool You've probably heard of it.



Okay..so switch to non scented chlorine bleach....got it.

Can I lower the CYA so I can lower the chlorine level?

[mr_clean]

I was just checking out the endless pool website and I think if you run your pool with second pump/turbo going for a awhile on high you would get the same aeration your looking for to adjust PH backup. These really move the water.
Another thing buy a chlorine float when you want to use tabs, putting tabs in skimmer is bad for equipment.

[Jeffm]

Mr. C,

Thanks for your input, but I don't have the secondary pump. Didn't get the jacuzzi option.

If you're thinking of the power unit that generates the flow. Yes, that does really move the water, but the 6HP hydraulic pump in the basement makes a bit of noise (working on enclosure).

Really the best option is a little PVC pipe I've already drawn up, and just putting that on the return fitting. Less power consumption and alot quieter.

I do have a float....and had the tabs in there from time to time, but I think I'm switching to the bleach, and will just use the float when I'm going out of town etc..

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[Jeffm]

Well, I'm not done yet...but I must say that the rate at which pH increases with good aeration is impressive. I went from 7.2 to 7.8 in like 3 hours.

The downside is a very humid room...

Looking forward to putting more time into this tonight.

[chem geek]

Too bad about the humidity. I didn't think about that since most pools are outdoors so the aeration doesn't have such side effects. The pH rise is fastest from the lowest pH -- so faster from 7.0 to 7.2 than from 7.6 to 7.8 -- so you can add acid whenever it goes up or just at regular intervals, whatever is convenient for you. The amount of acid it takes to lower the TA is independent of how frequently you add it or how far you let the pH go up between additions -- adding the acid before the pH goes up a lot just makes the process go faster but doesn't change the cumulative total amount of acid needed.

In 3000 gallons, every 100 ppm reduction in TA needs a cumulative total of 77 fluid ounces of Muriatic Acid (31.45% Hydrochloric acid) though you obviously don't add that all at once since you don't want the pH to go below 7.0. That should give you some idea of how you are doing and how much you'll need -- assuming the TA test was accurate.

To go from a pH of 7.5 to 7.0 at a TA of 400 requires 33 fluid ounces of acid and will lower the TA by 44; at a TA of 300 it requires 26 fluid ounces and will lower the TA by 33; at a TA of 200 it requires 18 fluid ounces and will lower the TA by 23; at a TA of 100 it requires 10 fluid ounces and will lower the TA by 13. That should give you a rough idea of what is required as your TA gets lower. I'm sure you'll get a feel for this as you proceed. You can see how it will take more frequent acid addition as you get to lower TA and you'll also find that the pH rises more slowly at lower TA (which is what you're really trying to get to). You could probably just get down to 80 and stop there and see how things go in terms of pH stability. I only mentioned 50 before thinking that your pool had a lot of aeration, but then realized you had high TA from the Soda Ash.

Richard

[Jeffm]

Well,l I was down to 250 ppm last night.

I modified my aerator pipe, so it fits underneath the cover. So, I can keep the humidity contained. The aeration and pH rise is much slower now. (I expected that) but wow...every surface of the inside of my sunroom has water on it from the previous night.

I also found another side effect of the aeration. Algae formation. Cl levels were about 3 ppm. I put in 1 cup of bleech for now, and guess I'll address the algae when I get done with the Alk.


Running the pump all day should get the pH way up again so I can put more acid in tonight when I get home.

[chem geek]

The aeration probably outgassed the chlorine faster as well, so yes, the chlorine level needs to be kept up or else algae can form. Too bad you can't aerate the water and get the TA lower before it gets added to your pool.

I wouldn't wait to address the algae. I'd hit it with chlorine now or else it will just get worse.