When to increase CH and a question about adding MA

[nobody291]

I think my test results are visible, please let me know if they're not. I did a pool water exchange a few weeks ago to reduce CYA and my CH dropped from 450 to 275. 275 is just above the minimum but outside the recommended range. Would you recommend that I increase CH to 350, or leave it as is? We resurfaced the pool about a year ago, in case that makes a difference.

On another note, I've read different things about using MA. I generally let pH rise to 7.8 or 8 before adding MA. I've seen guidance saying I should only add it a quart at a time. Is that reasonable? The most economical MA for me is 14.5%, so it's fairly weak as MA goes. I slowly add it in the deep end so that it gets distributed by the jet there, have the filter pump running, and then do some brushing to make sure the MA doesn't "pool" in one spot. Any thoughts on how much to add at one time? pH is at 8.2 today, so I will be adding a gallon of MA total.

Thanks for making this site available, it's a great resource.

 

[jimbethesda]

What’s your fill water CH level? Do you have to add water (either manually or by auto fill) regularly, or do you have to let water out of your pool due to rainfall?

 

[Dirk]

I would add that much MA in a few doses, a few hours apart, just to play it safe. Though I suspect it doesn't really matter. When I have to add MA in my 12K pool, I rarely need to add more than a cup or two. pH usually likes to live around 7.8 or higher. The more you try to force it down, the more MA you'll need. And it's not linear: going from 7.8 to 7.6 takes way more than twice as much as going from 7.8 to 7.7 does. That logarithmic scale gets worse and worse the lower you try to force it. And you could mess with TA by doing that, too. Are you paying attention to CSI? You should be. If you can maintain a good CSI number with a pH of 7.8 or 7.9, then do that. You'll see that your MA consumption goes waaaay down. When I use 7.8, my TA takes care of itself.

What does your fill water CH look like? CH doesn't evaporate, so it will build up in your pool. If you have hard water, I'd be tempted to leave CH alone and let it build up on it's own. That would postpone the inevitable water exchange a bit. If you're comfortable exchanging water, and are at all worried about your new-ish finish, then bump the CH, especially if the finish warranty calls for a minimum amount of CH. Protecting the warranty is almost as important as protecting the finish. The right amount of CH does both.

 

[nobody291]

Thanks for the detailed reply.

And you could mess with TA by doing that, too.

I should've added that I'm trying to bring TA down into the recommended range, then hopefully the pH will prove more stable. The pool warranty requires pH to remain between 7.2-7.6 which seems sort of tight.

Are you paying attention to CSI?

Yes, with pH of 7.4 it's -.21, at 7.8 it's .17.

What does your fill water CH look like?

It's very low, 25 is my test result, but the color change is very slight when the reagents are added. TA of the fill water is 140, so I guess that led to my TA rising during the water exchange. The warranty just requires CH of 200-400, so it's probably better to leave it alone. Is the risk of keeping it out of the recommended range that the water will leech calcium from the finish and weaken it?

 

[nobody291]

What’s your fill water CH level? Do you have to add water (either manually or by auto fill) regularly, or do you have to let water out of your pool due to rainfall?

I have to add water...fill water CH is 25. In the winter/spring, we get some rain and it's normal to lose some water through the pool overflow drain. But, the rest of the year is dry here.

 

[duraleigh]

Are you getting that CH 25 from a spigot that goes through a water softener.........that is VERY unusual for CH 25 to occur naturally.

 

[Dirk]

Thanks for the detailed reply.



I should've added that I'm trying to bring TA down into the recommended range, then hopefully the pH will prove more stable. The pool warranty requires pH to remain between 7.2-7.6 which seems sort of tight.



Yes, with pH of 7.4 it's -.21, at 7.8 it's .17.



It's very low, 25 is my test result, but the color change is very slight when the reagents are added. TA of the fill water is 140, so I guess that led to my TA rising during the water exchange. The warranty just requires CH of 200-400, so it's probably better to leave it alone. Is the risk of keeping it out of the recommended range that the water will leech calcium from the finish and weaken it?

If CH is low, yes. If high, then the risk is calcium coming out of solution and adhering to the finish, otherwise known as scaling.

That said, CSI is the better indicator to keep either of those from happening. It is a combination of CH and pH (and several other factors, including water temp) that determines the health of your finish, and specifically what the calcium is going to do (CSI = Calcium Saturation Index). CSI accounts for all of the factors. Focusing on any one or two of the factors does not. It's more important to maintain good CSI, even at the expense of the other factors (though ideally, everything stays in range). If it were my pool, I would allow pH to rise to 7.8, because a CSI of -0.17 is a little better for the finish than -0.21, and the side benefit would be less battling with pH.

Yes, you want to maintain the levels that protect your warranty. But the long-term effects of good or bad CSI will not become apparent until well after the warranty expires. You'll get "stuck with the bill" 10 or 20 years from now, not the warranty holder. It's a tough call.

I'm not saying the difference between .17 and .21 will cost you any number of years of finish longevity. I'm approaching this topic for my pool the way I am because I'm interested in stretching out the life of my new finish as long as possible. I need this finish to outlast me, and it's going to be close! So I eek out every minute of life I can (for both of us!). Your goals might be different, so you figure out what tradeoffs work for you.

 

[nobody291]

Are you getting that CH 25 from a spigot that goes through a water softener.........that is VERY unusual for CH 25 to occur naturally.

The sample I checked was from the fill line dedicated to the pool (taken as it was filling the pool). I'm pretty sure that the softener is plumbed so every water source for the house is softened. Should I try bypassing the softener and check a sample that way? Would it make a significant difference?

If it were my pool, I would allow pH to rise to 7.8, because a CSI of -0.17 is a little better for the finish than -0.21, and the side benefit would be less battling with pH.

Just to be clear, my CSI is -0.21 with a pH of 7.4 and +0.17 with a pH of 7.8. The Pool math app suggests a target of -0.6 to +0.6 for me, should I target a smaller range than that?

good or bad CSI will not become apparent until well after the warranty expires.

That brings up another question I've wondered about. Should I really spend that much time trying to manage the water chemistry based on the warranty? That warranty requires fairly precise levels on mulitple parameters that are hard to meet simultaneously. For example, it requires a free chlorine level of 1-3ppm and CYA of 50-80ppm. Obviously those ranges aren't compatible with what you guys have taught me here. Does anyone have experience getting repairs done under their warranty? Will the pool installer just look for a loophole in your monthly test results where one parameter was outside what the warranty required? I wish I would've been more knowledgeable about this before we did the installation and I would've questioned the warranty.

 

[Dirk]

My bad on the +0.17. The closer to 0.0 the better. We generally advise to run a little negative if you have an SWG, if not, then closer to zero. I would play with the pH to get CSI to zero, and see if that solves some of the other MA dosing issues.

If you have a water softener, all indoor fixtures should be soft water. But all outdoor fixtures should be hard water (not on the soft water circuit). I added an exterior soft water hose bib near my pool pad, specifically to feed the pool's auto-filler with soft water. Maybe yours was done the same way. So the first thing to determine is if your filler is connected to hard or soft water. Test CH from three sources: the auto-filler (which you've done), a bathroom sink and an outside hose bib (from the bib, not the hose). If CH is all the same, your house is an anomaly, and/or your plumbing is feeding soft water to your garden (which is not great). If the CH is higher at the hose bib, but the bathroom sink and your auto-filler are the same, then your auto-filler is being fed soft water (which is a good thing). Then at least you'll know what's what.

Regarding the warranty conundrum, that's what I meant by "tough call." I believe TFP guidelines are best for my finish long term. My finish is still under warranty, but the installer did not impose any chemistry restrictions, so I am free to follow TFP numbers. You've got the opposite situation. And yes, some installers or manufacturers will site out-of-spec water conditions to void your warranty. So what is a consumer to do? If their numbers and TFP numbers are close, follow theirs for the length of the warranty and switch to TFP numbers when the warranty expires. For that number of years, you won't be shaving much if any off the total longevity. If their numbers are significantly different, then you'll have to pick one or the other, or fudge it. Fudge it how? I would get everything but pH set within their ranges. Then adjust pH to satisfy the CSI, as close as possible to zero. If I needed a warranty repair, I'd adjust the pH into their acceptable range. If they then came out and tested my water for warranty compliance, I'd be within all ranges. If they needed monthly logs, I supposed I'd have to keep "two sets of books." Then after the repair, I'd readjust pH to satisfy a good CSI and go on my merry way. Which would be straight to h-e-double-hockey-sticks for even suggesting such a deceitful thing! Like I said, tough call. It can be a bit of a roll of the dice and you have to pick your poison.

 

[Dirk]

By the way, the Pool Math app has a great tool for working out CSI. You can call up the CSI section of the Overview page, and it will show you the most recent levels that affect CSI. You can then adjust any of those parameters and watch what happens to the CSI number. This is a great way to learn how each parameter affects CSI, and which is best to adjust for any given goal.

 

[duraleigh]

Would it make a significant difference?

Absolutely! Test before your water source gets to the water softener. If you can feed that as your source, it may be better and could actually preclude you having to add any Calcium at all.

As an aside, but still connected, I disagree with dirk's emphasis on CSI. If you have access to CH 25 refill water, CSI will simply never be an issue....NONE!

Topic for another thread but I feel strongly that CSI will never enter your interest in pool water management.

 

[Dirk]

291, I gotta defer to Dave (a TFP Expert) when it comes to pool chemistry. He has way more knowledge about this stuff than I do. The fact that you're here at TFP, and asking all the right questions, will translate to great success with your pool!

 

[nobody291]

Thanks to both of you for taking the time to help me. I'll do more testing of water sources around the house and come back with more questions!

 

[duraleigh]

I'll be surprised if that CH of 25 is naturally occurring but, of course, it could be, I guess. Let us know when you find out and we can suggest a good path for you.

 

[nobody291]

That was an interesting exercise. As you suspected, our un-softened water has a higher CH...it's 300. I measured the bathroom faucet and it matched the 25 I measured for the pool fill water a few days ago. We have two hose bibs in our backyard. One seems to be hooked to soft water (this is where the pool fill water is plumbed to come from), the other provides hard water and is connected to the same supply line as the sprinklers, so it's nice to know that our sprinklers are not using soft water. TA for the soft water measured 170, hard water measured 150.

Any suggestions based on my circumstance?

 

[Dirk]

Not really. You've got a great setup to keep the pool's chemistry in check. Dave can advise about what to do with your CH, now that you know what's what.

 

[Dirk]

PS. Now that you know you've got an outdoor soft water bib, you can clean the windows and wash the car with that, without all those water spots getting left behind!

 

[Dirk]

Hmm, @duraleigh didn't make it back today. Your 275 is nothing pressing. If he doesn't come back with a better answer in a day or two, then raise your CH to get it in range. Your fill CH is essentially zero or close to, and because you're getting rain that washes some of the CH away, I'd say CH accumulation is a non-issue, so you won't benefit from stalling the CH dose. So bring it up to your target range. If there's a number that satisfies both TFP guidelines and your warranty, then that's your target.

 

[duraleigh]

Any suggestions based on my circumstance?

Sure. Why not use your fill water to control buildup of your CH. In other words, fill your pool from the CH 300 water if you need to raise CH or from the 25 CH fill water if you need to lower it.

275 is just fine for your pool

 

[nobody291]

Thanks again for the help and suggestions!