CH increasing after refill

[Archilla]

Hey everyone,

I've been lurking around here for knowledge since we bought our house about a year ago, and it's been really valuable to help me figure out issues and develop a good maintenance routine. The Pool School is especially helpful. In any case, I did a complete drain/refill about 4 months ago (mid May) because the CH had been really high since we bought the house, and there had been white flakes in the water (which I assumed were calcium deposits) which I could never get rid of. After I did the refill, it took me a couple of weeks to get everything balanced (mainly the alkalinity), but since then the water has been clear and beautiful, and the water balance has been basically very stable except for two things:
1) I need to add 2 cups of 20 Baume acid every other day to keep the pH in range (add at 7.8, brings it down to 7.5). Is this typical, and if so, is the constant acid requirement due to the aeration from the spillover spa and the SWG? Alkalinity has been very stable at 90.
2) The calcium hardness has been increasing rapidly. The fill water CH was 270; it is now up to 460, so it has been increasing roughly 50 ppm per month. Does this make sense? The only reason I can think to explain this is evaporation, but while it has been hot this summer, I really don't understand if this alone can explain the constant CH rise.

Load is light (just a few people swimming, and mainly on weekends); otherwise the water looks great. But at this rate, I'll be back up to the previous CH levels within a year...

Latest test results from last weekend:
pH: 7.7
FC:4
TC:4
CC:0
Alk:90
CH:470
CYA:60

Thanks in advance for any help.

-Ruben

 

[jblizzle]

Welcome to TFP!

Sounds like you have a pretty good handle on things ... Although draining for CH is rarely an issue if you keep close tabs on the pH.

Your acid demand sound reasonable due to the SWG and spillover. You may be able to reduce it if you bring the TA down further closer to 60-70ppm as we recommend.

The only way for your CH to rise is by adding increaser or evaporation ... that does seem pretty quick. A cover could help flee the evaporation rate.

Posted from my Droid with Tapatalk ... sorry if my response is short

 

[linen]

Welcome to tfp, Archilla

The calcium hardness has been increasing rapidly.

Do you or did you have calcium scale on the pool surfaces? If yes, then it could be that you are slowly removing/dissolving it, and if you are, it has to go somewhere... though 50 ppm a month would be faster then I would expect, especially since your csi is not real low.

By any chance are you using cal-hypo as a chlorine supplement?

 

[jblizzle]

Oops. How did I forget to ask about the cal-hypo?

Posted from my Droid with Tapatalk ... sorry if my response is short

 

[Archilla]

Thanks for the replies.

The only chlorine source since the refill has been the SWG. Prior to the refill I had been using liquid chlorine due to a failed SWG cell, but I replaced the cell at the same time as the refill and have not done any additional chlorination since.

There may well have been calcium scaling on the walls previously, especially since I saw what I thought was calcium precipitate in the water before the refill, however I did a light acid washing and thorough scrubbing of all of the surfaces when the pool was drained, so I would expect that would have removed or at least reduced any scaling.

By the way, the increase in the CH since the refill has been consistent; it has been increasing at a steady rate over the last 4 months every time I test the water. If calcium was being pulled off of scaling on the walls, at some point the rate of increase of CH should slow down I would guess.

Anyway, I'm not sure if my quick math is correct, but my rough estimate is that if evaporation was the only source of CH increase, with the fill water CH at 270, about 2800 gallons would need to evaporate each 2 weeks to produce an increase of 50ppm in a 15k gallon pool. I've not tried to calculate the rate of evaporation, but 2800 gallons in 2 weeks sounds much higher than actually feasible...

Hence my confusion.

Thanks in advance for any additional ideas.

-Ruben

 

[UnderWaterVanya]

Anyway, I'm not sure if my quick math is correct, but my rough estimate is that if evaporation was the only source of CH increase, with the fill water CH at 270, about 2800 gallons would need to evaporate each 2 weeks to produce an increase of 50ppm in a 15k gallon pool. I've not tried to calculate the rate of evaporation, but 2800 gallons in 2 weeks sounds much higher than actually feasible...

What are your pool dimensions? Roughly speaking you would be losing between 1/6 and 1/5 of your water every two week if the gallons info is accurate. That seems pretty high but hard to judge without dimensions.

 

[Archilla]

UnderWaterVanya,

Rectangular, about 30 x 15 ft, so the surface area is relatively large for the capacity (because it is pretty shallow, 5.5 ft at the deepest point). Even with the large surface area, I can't imagine that I'm losing that much to evaporation.

A coworker of mine that lives a few miles away and has a pool of the about the same capacity has not seen any significant increase in CH for a while, although his numbers are from Leslie's, so perhaps not completely reliable numbers. Leslie's doesn't measure CH unless you specifically ask them, so I'm not sure how often this guy is having it checked, but anyway, he seems to be having a much different experience than myself on this issue.

I remain confused. Guess I'll keep an eye on the CH for a while longer and see if the rate of increase ever slows down...

-Ruben

 

[Archilla]

One more thing I can add: I have not backwashed the filter at all since the refill 4 months ago. The filter pressure has only increased by about 2 psi (I use a leaf canister on the Navigator, and a skimmer sock, so most of the stuff gets caught before passing through to the filter), so I don't think it is necessary. At this rate of pressure increase, I'll likely just backwash at 6 months and clean the filter at 1 year, more due to time than filter pressure. That said, if I were backwashing more regularly, the water replacement/dilution from backwashing would help to offset any CH increase from evaporation.

So now I'm wondering if I should be backwashing more frequently, not because the filter needs it, but because it may keep the CH from increasing as quickly.

Thoughts on this one?

-Ruben

 

[UnderWaterVanya]

So now I'm wondering if I should be backwashing more frequently, not because the filter needs it, but because it may keep the CH from increasing as quickly.

Thoughts on this one?

Does your filter have a waste setting? If so you can dump a little water now and then just as though you backwashed. The filter does better when a bit dirty.

-sent with Tapatalk 2

 

[Archilla]

No waste setting on the filter, just backwash. There is a hose bib on the output side of of the pump, so I suppose I could draw off water there without backwashing out the DE.

Something else just occurred to me recently that I did not mention in the earlier posts. I apparently have high metal content for some reason, as I've had problems with a fading endpoint on the CH test, even since shortly after the refill. For a while I was fine using the "add 5 drops of R-0012 first" method, but in the last month or so, even that is not enough to prevent the fading endpoint, so I've had to use the 50% dilution with distilled water method. This brings me to a few new questions...
1) Where might the metal content be coming from, and should I be worried? Other than the annoyance of the fading endpoint on the CH test, there are no obvious other problems, i.e. the water looks fine and there are no unusual stains showing up. The only source I can think of would be the heater, but pH has been closely maintained since we've owned the place. Fill water is from the local water district (their water quality report is attached).
2) What are my options if the high metal content is an issue?
3) Could this be affecting the CH reading to be erroneously high?

As of my last test, CH is now up to 500ppm.

Thanks again,
-Ruben

 

[ping]

I'm right on the boarder of LA/OC and have a pool roughly the same size of yours. I have been losing about 500 gallons a week the last couple of months. My pool is almost 2 years old and my CH has gone from 220 at start up to 270 as of last months test. I don't see you losing enough water to evaporation to raise your CH level that fast, so something else should be happening. I'm sorry that I can't say what that something is, but I think you should be able to rule out that evaporation is causing your problem.

About the fading endpoint with the CH test, I have had the exact same problem from day 1 with my pool water. All tests that I had from the PS in the past never showed any metals in the water and I never have had any other issues with metal in my water. This is the only symptom that there is any metal in my water. I add about 90% of the expected amount of R-0012 first then continue with the test as usual. Make sure you continue adding the R-0012 until the test turns blue. You might need to add more than a few drops when the test turns purple, just make sure you are swirling a lot between the drops. The speedstir really helps to make this test easier.

 

[Richard320]

It sounds normal to me. Your acid consumption is about the same as mine, and I don't have a SWG. But I am lifting scale off the walls; I have been for almost two years. I figure by next Spring it ought to be all gone.

I'm not sure if my CH has ever been as low as yours is now, and I work on it. Not all the time, put frequently I use pool water on my lawn, and refill it with fresh to reduce the CH. It has the side benefit of lowering CYA, which then lets me use trichlor pucks when I leave town. The pucks also are acidic, and when they're in the pool I don't need so much muriatic acid.

I connected a flexible tube to the closest downspout so it runs into my pool during rainstorms. The area it drains is such that 1" of rain gets me 3" in the pool. Every setup will of course be different. When a storm is brewing I start draining the pool. The first rain tends to carry a lot of dust into the pool. My setup runs into the spa, which i shut off during rain. Then it acts like a settling basin. When I get around to it after the storm has passed, I just move the valves so the filter is only on the spa and it clears it in a hurry.