Living with 2176 ppm CH fill water

[BrandonWhite]

Hi,

My fill water comes from a very deep (~600 ft) private water well. The water that it produces is off-the-charts high in calcium hardness. 127 grains/gallon the last time I measured it -- very tedious to count that many titration drops! So as you can imagine the CH of my pool is always quite high. And as if that is not challenge enough, the climate here is hot and usually very dry. This past month I've been using about 800 gallons of water/week to keep up with evaporation.

I do have a heavy-duty water softener, but I want to avoid using it for the pool. It costs me about 30 lbs of salt for every 700 gallons that flows through it (plus a regen cycle). And then I'd simply be trading CH for salinity build up over time.

I'd appreciate some guidance from the TFP experts on water chemistry targets I should be shooting for, given my unusual case.

I've been using PoolPal daily to help me with calculations and CSI tracking. Here's my latest measurements:

FC: 3.0
CC: 0
pH: 7.2
TA: 95
CH: 1250
CYA: 65

Notes:
FC: I realize it needs to be higher per recommended FC/CYA ratio. Algae and clarity have not been a problem. The water's been great.
pH: I'm currently in the process cycle of reducing TA, so I've been adding acid to 7.0 nightly and running the waterfall continuously. pH rises to about 7.2-7.3 the next day.
TA: Was at about 130 after the last fill water top-off. Currently trying to reduce to 70 with good progress thus far.
CH: This has been very difficult to test with the Taylor K2006. I have a terrible case of the vanishing endpoint or whatever they call it. Even doing their special procedure of pre-adding the reagent, I continue to get a blue endpoint that seconds later turns purple. I expect the CH is higher than what I'm interpreting from the drop test.
CYA: Down from 230, yay!

Observed water quality: Fantastic. Very clear. No algae growth. No issues at all with scale.

Q: Should I strive for a lower pH to keep my CSI close to zero (balanced), below the norms recommended by TFP? What is the lowest I should ever allow pH to reach (assuming CSI is always balanced)?

Q: I'm wanting to add borates to 50ppm (test kit on the way). The sticky post on adding borates says to ask if CH and/or TA of fill water is high, so I'm asking ! What special procedures or conditions do I need to apply before or after adding borates?

Thanks y'all!

 

[chem geek]

Yikes! 127 grains/gallon is 2174 ppm! You wrote a CH of 1250 ppm so your fading endpoint problem may be having you underestimate the true CH. With your very high CH, I'd use the 5 ml water sample to save on drops where each one would then be 50 ppm. I would start by adding 20 titrant drops before adding calcium buffer and indicator dye to reduce the fading endpoint problem since you know you've got CH above 1000 ppm.

Your water quality at the lower FC/CYA ratio is OK possibly because your water is poor in algae nutrients, but you should follow the Chlorine / CYA Chart unless you intend to use an algaecide or measure algae nutrient levels (e.g. phosphates), but we don't have charts to tell you the FC/CYA to use in that case.

Because of your low pH and your getting the TA lower, your CSI (using 2174 ppm CH) is between +0.2 and +0.3 which is why you aren't seeing scaling. We usually only see scale in pools at +0.7 or higher, especially +1.0 or higher. If your pH were to rise to 7.7 or higher, then you might start seeing scaling. You do not need to have your CSI at zero. Having it be positive is not a problem so long as you aren't getting scaling. The biggest risk area would be in an SWG cell but you don't have that. The next biggest risk area would be in a gas heater since the heat exchanger is roughly 30ºF hotter when on so if your pool was 85ºF and you were heating it then that could be a problem even at a pH of 7.2 (scaling at hot temperatures in heat exchangers may be seen starting around a CSI of +0.3). Do you have a gas heater you intend to use?

Why do you want to add borates to the pool? If the pH isn't tending to rise quickly then why add borates? I don't think high CH matters with the borates. As for higher TA and having fill water high in TA the borates won't change the amount of acid you need to add regularly to keep the TA down but may space out such acid additions (i.e. you add more each time, but less frequently).

 

[BrandonWhite]

Thanks for the quick and detailed reply!

I'd use the 5 ml water sample to save on drops where each one would then be 50 ppm. I would start by adding 20 titrant drops before adding calcium buffer and indicator dye to reduce the fading endpoint problem

10-4. I will do that this afternoon. The Taylor instructions only suggest a 10ml sample to get a 25ml drop step. A 50ml step sounds great. However, do I need to reduce the buffer and indicator by an appropriate amount too?

you should follow the Chlorine / CYA Chart unless you intend to use an algaecide or measure algae nutrient levels (e.g. phosphates)

I'm not opposed to running higher FC levels. But it seems like each day lately my FC drops to about 1 ppm at the end of the day, regardless of if I liquid chlorinate to 3ppm or 6-7ppm the night before. Adding nearly a gallon of bleach daily is something I'd prefer to avoid. A pint or even a quart I can live with. I have to hope that this is a the worst it will be right now. I'm certainly open to checking on phosphates and also using an algaecide. What would you recommend as a test kit and frequency, and an algaecide product?

Do you have a gas heater you intend to use?

No. There is no spa or heat system.

The biggest risk area would be in an SWG cell but you don't have that.

Yeah but I'd really like to replace my UV lamp with one. Do you think SWG is a non-starter for me? Can I not keep the CSI balanced and avoid scale or other issues with the SWG? Please educate me. Daily manual dosing of liquid chlorine isn't an attractive long-term solution for me. If SWG is impossible, I will likely go with Stenner pump. But then I still have to go buy and store fairly large amounts of liquid bleach (boo).

Why do you want to add borates to the pool?

Because it sounds interesting, novel, and cool. Primarily for sparkling water and skin feel. I also like the potential algaecide effects. If it helps kill the scorpions and spiders quicker, even better. If it helps cut down on the frequency of TA reducing, I'll take that too! Quantity of acid isn't an issue for me -- quantity of liquid chlorine is my main gripe.
Before I put any borax in I'm waiting for the borates test kit to arrive though. The behavior of the pool in the 2 months so far that I've owned it makes me suspect that it could already have some appreciable amount of borates. The pool exhibits all the qualities that are touted for borates (not sure on skin feel though. Nothing to compare it to). It could be in my head though.

 

[chem geek]

The Taylor instructions only suggest a 10ml sample to get a 25ml drop step. A 50ml step sounds great. However, do I need to reduce the buffer and indicator by an appropriate amount too?

Since your magnesium hardness is likely high, I'd use the same number of calcium buffer drops as with the 10 ml sample (10), but use 2 drops of R-0011K indicator dye.

I'm not opposed to running higher FC levels. But it seems like each day lately my FC drops to about 1 ppm at the end of the day, regardless of if I liquid chlorinate to 3ppm or 6-7ppm the night before. Adding nearly a gallon of bleach daily is something I'd prefer to avoid. A pint or even a quart I can live with. I have to hope that this is a the worst it will be right now. I'm certainly open to checking on phosphates and also using an algaecide. What would you recommend as a test kit and frequency, and an algaecide product?

Up to you, but you run the risk of algae growth (which looks like unusual chlorine demand at first and may not be visible initially) if you aren't keeping at least the minimum FC/CYA level.

No. There is no spa or heat system.

That's good so your risk of scaling is minimal.

Yeah but I'd really like to replace my UV lamp with one. Do you think SWG is a non-starter for me? Can I not keep the CSI balanced and avoid scale or other issues with the SWG? Please educate me. Daily manual dosing of liquid chlorine isn't an attractive long-term solution for me. If SWG is impossible, I will likely go with Stenner pump. But then I still have to go buy and store fairly large amounts of liquid bleach (boo).

You have a UV lamp? If it's powerful, then that will consume chlorine. Turn it off and see if that changes your chlorine demand.

An SWG is not really an option for you because I think it will be way too hard to prevent scaling in the SWG cell even if you were to use borates. You'd have to keep your TA and pH low and that will take a lot of acid and may be too cumbersome to do. You'd probably need to figure out a way of getting calcium out of your pool to use an SWG -- either trucked-in water, reverse osmosis, use of a high-capacity (or frequently regenerated) water softener, etc.

The behavior of the pool in the 2 months so far that I've owned it makes me suspect that it could already have some appreciable amount of borates. The pool exhibits all the qualities that are touted for borates (not sure on skin feel though. Nothing to compare it to). It could be in my head though.

There won't be any borates in the water unless you've added it. There isn't any in fill water.

 

[BrandonWhite]

- I did as you suggested with the CH test: 5ml sample, pre-add 20 titrant drops, then 10 buffer drops, *two* indicator drops, then proceed as usual with the titrant. My solution immediately turned the dreaded purple as soon as the indicator went in. I still fought with fading endpoint, but it was much improved from my prior experiences. And certainly I appreciate a lower overall drop count. As I continued to add titrant, the solution would turn blue, then within 10s or so (at first) would gradually shift back to purple. With each successive drop the fade-back-to-purple would take longer. Overall it took me about an hour to conduct the test. I'd add a drop, see the blue, record a tick, then go play with the kids in the pool. Come back, observe purple, and repeat. I called it done after the blue held for about 30 minutes. I recorded 20 (pre) + 13 (post) drops for a grand total of 1650 ppm CH.

Could you explain what is the significance or action that occurs by pre-adding titrant? I understand that it has something to do with the iron and/or manganese ions but why does the pre-add improve the fading endpoint vs. post-add as normal?

- Regarding FC. Out of respect and trust in you and this forum, I will give it an honest try your way. I added a gallon of 10% liquid chlorine at dusk (PoolPal called for 126 oz). I also disabled my UV lamp. After 30-60 minutes I did a DPD-FAS test and got 8.0 FC on the money, and < 0.5 CC (I need help interpreting the CC test. When I add the drops my milky white solution gets this extremely slight pink tint -- barely noticeable save for the fact that you just saw it in it's whiter state. The subsequent titrant drop puts it back to completely white).

At dawn I tested again so we could see what chlorine demand is looking like. FC: 7.0 - 7.5 ppm (ocl of 0.5-1). CC behaved the exact same as the night before (0.0 - 0.5ppm). So as I understand I should be good on chlorine demand, algae pregrowth, leftover ammonia from my recent BioActive treatment, etc.

I will test FC again this evening before any chemical additions and report back.

SWG I understand and appreciate your guidance. I will live with high CH and liquid chlorine for now and defer the SWG. Perhaps in a year or two I will expand my 128k grain softener to a dual tank system and use the softened water as fill for the pool. Trucking in is cost prohibitive at $100/2kgal here. I will also continue to research possibly a DIY high-pressure high-flow RO system as I have interests in that beyond the pool.

There won't be any borates in the water unless you've added it. There isn't any in fill water.

Right, sorry, I meant that the previous owner may have added borax. I'll know soon enough.

 

[chem geek]

I think you meant a 5 ml water sample, didn't you?

The fading endpoint is caused by metals in the water and the titrant drops you add are EDTA which among other things sequester that metal. When you add that before the indicator dye, you tie up those other metals so that they don't interfere with the test. If you wait, then what happens is that the later drops of EDTA bind to calcium at first but then other metals replace the calcium that then recolors the dye. The metal is slow to bind to EDTA because you've added the calcium buffer (which is sodium hydroxide) that raised the pH to precipitate out magnesium, but that also forms metal oxide-hydroxide and that's slower to react and bind to EDTA. By adding the EDTA before you raise the pH with the calcium buffer, you bind the metal ions early and more quickly to reduce the fading endpoint.

You are doing the CC test correctly -- you have <= 0.5 ppm CC. It's probably <= 0.2 ppm CC but you could only test that low using a 25 ml water sample (and it's not worth it since it's not a problem).

Losing 0.5 to 1.0 ppm is actually on the higher side at the lower FC level, but it's not a disaster and you're close to the resolution of the Taylor test.

 

[BrandonWhite]

I think you meant a 5 ml water sample, didn't you?

Yes! I used a syringe to measure it too! Thanks for catching that. I edited my previous post for anyone that comes along later.

Thanks for the explanation, very helpful.

So after a day of heavy sun and extreme UV (according to the weatherman) my FC measured at 5.5ppm. This required 45oz of 10% bleach to bring back up to 8ppm.

So I figure at this rate I'll be going through 11 gallons of 10% bleach every month. At $3.76/gal, that's about $41/mo. That seems like a lot, especially for my smaller 15kgal pool. Is this normal for TFPC?

 

[chem geek]

45 ounces of 10% bleach in 15,000 gallons would be 2.3 ppm FC. 2-3 ppm FC per day is a normal daily chlorine usage amount. You can cut that down to around 1 ppm or less if you use a mostly opaque pool cover. Your bleach is a bit pricey which is part of the problem. I get 12.5% chlorinating liquid at around $4.33/gallon and that isn't particularly inexpensive, but would be equivalent to $3.46 for 10%. If you are able to get Great Value Bleach at Walmart for $2.94 for 121 fluid ounces and that's 8.25% bleach, then that would take 52 fluid ounces for the same 2.3 ppm FC rise so would be equivalent in cost for 10% as $3.60 per gallon (assuming the 10% is "Trade %" where the 8.25% bleach is equivalent to 8.64% Trade). You may be able to find deals for even less or some vendor that sells carboys or 4 gallons at a time for less using reusable bottles.

 

[BuckeyeChris]

I would be interested to see, With the pump running all night, an oclt with uv off, and the next night, same starting fc, oclt with uv engaged. Might give you an idea how much FC loss during the day was from uv.

 

[BrandonWhite]

45 ounces of 10% bleach in 15,000 gallons would be 2.3 ppm FC. 2-3 ppm FC per day is a normal daily chlorine usage amount.

Ok. I will deal with it then. I continue to search for a local supply of bulk quantity liquid chlorine (I chlorine inject into my well water too, but much less than the pool uses) as well as salt (for softening). Driving over to the big box stores has been my best bet so far.

On the upside, the economics of SWG is looking better for me! I'm really interested primarily for the automation aspects. If it's even just a little cheaper, and back-of-the-envelop it appears so, well that's icing on the cake!

I would be interested to see, With the pump running all night, an oclt with uv off, and the next night, same starting fc, oclt with uv engaged. Might give you an idea how much FC loss during the day was from uv.

Very good idea. I'll give it a go.

 

[chem geek]

As shown in Economics of Saltwater Chlorine Generators, you'll want to get an oversized unit so the Intellichlor IC40 (not the IC20) or the Hayward T-CELL-15 (not the T-CELL-9). They will last longer than the smaller models but for only a little more expense up-front.

If you have soft stone around your pool, you may need to seal it -- many pool builders in Texas don't install SWCG systems because of the soft stone that they use around pools. Saltwater splash-out and evaporation can damage soft stone and concrete.

 

[BrandonWhite]

As shown in Economics of Saltwater Chlorine Generators, you'll want to get an oversized unit so the Intellichlor IC40 (not the IC20) or the Hayward T-CELL-15 (not the T-CELL-9).

Great info in that thread, thanks. Indeed I've been eyeing the IC40.

If you have soft stone around your pool, you may need to seal it -- many pool builders in Texas don't install SWCG systems because of the soft stone that they use around pools. Saltwater splash-out and evaporation can damage soft stone and concrete.

10-4. The only stonework I have is the coping around the perimeter of the pool, and my guess is that it's limestone. Sealing it makes good sense.

I would be interested to see, With the pump running all night, an oclt with uv off, and the next night, same starting fc, oclt with uv engaged. Might give you an idea how much FC loss during the day was from uv.

I did this experiment last night. 2ppm loss oclt with UV on and pump running all night, vs. 0.5-1.0ppm oclt from 2 nights ago (pump off, UV lamp off). HOWEVER, at dusk when I added 64oz of chlorine to get back to my 8 ppm target for the day (but with the UV off at this point), when I came back an hour later to turn on the pump and UV lamp for the experiment I went ahead and did a test and was surprised to only have FC:6.5 and CC:0.5 (definite CC this time. clearly a pink tint with a return to white after 1 drop). I pondered this a bit then proceeded to add 32oz of chlorine. 30 minutes later tested and got FC:9; CC:0.5. I unintentionally overshot my 8ppm target. So I don't know if my first chlorine dose one of the jugs was substantially weakened, I made a mistake, or got a sample before the water was thoroughly mixed. In hindsight I should have done a another test from another part of the pool before I added chlorine.

I might repeat this experiment at a later time, and try to do a better job controlling the variables. Did my UV lamp eat up 1ppm more than with it off? I don't think I can say. I do know that my pool gets a *ton* of UV exposure from the sun, so I'm not really getting the point of the UV lamp. I'll probably unplug it again, especially since it is real finicky about not wanting to turn on when I run my pump at low RPM.

 

[chem geek]

The UV lamp uses UV-C radiation for disinfection so while that still does breakdown chlorine the primary purpose for the UV is to disinfect against pathogens that chlorine doesn't effectively handle, particularly the protozoan oocyst Cryptosporidium parvum. We don't worry about that pathogen in residential pools since it isn't already in soil and air nor that common in people. It's more of an issue in commercial/public pools where one infected person with diarrhea can infect dozens or more over many days to weeks in a pool since chlorine doesn't inactivate this quickly (especially not with CYA in the water). So I agree with you that there isn't much point in an outdoor residential pool because certainly for the purposes of oxidation you've got plenty from chlorine and sunlight (producing hydroxyl radicals from chlorine).

Normally UV systems are sized for disinfection so the amount of chlorine loss will not be noticeable. If the UV is sized for oxidation (technically breaking apart molecules into smaller parts, not really oxidation per se) then that would usually result in a noticeably higher chlorine usage/consumption.

 

[BrandonWhite]

The UV lamp uses UV-C

Ah yes, I see what you mean. Different wavelength than good-old sunlight.

I think I may have found the culprit this weekend -- green slime inside the wall fountain return. When this is disabled and the return jets are the only path back, water sits inside the fountain all the way up to the top. It get's nice and *really* warm too. I sprayed straight 10% chlorine into the opening and onto the algae I could actually see on the stone.

I'm sporadic as to when I run the fountain. Usually when the kids ask for it. Days when I didn't run it, my CC was dead zero at my test at dusk vs a strong 0.5 ppm when I did run it.

What's the recommended practice with these things? The only thing I can think to do is to adjust my return valve to just keep the fountain slightly flowing whenever the pump runs. It would be nicer though if the thing would drain empty when not actively flowing.

 

[BuckeyeChris]

I open up the water features once a week for an hour. I guess you could put some bleed valves or something right where it branches from the filter. Which...sounds harder than just running them every once in a while.

 

[JamesW]

Try doing the calcium test with a diluted sample and multiply to get the actual.

1 part distilled water/ 1 part pool water multiply by 2
3 parts distilled water/ 1 part pool water multiply by 4 etc.

Does your supply water contain any metals such as iron, copper or manganese?