Consensus on acid injection - before SWCG or after?

[e_sully]

Installing an acid injection system (Hayward AQL-CHEM4-ACID but without the Hayward control, just manual dosing using schedule on Aqualink). Will be using 1:4 diluted 31.45% acid (so about 8%). Searching through the forum, I see the opinions over the years have varied. Some frequent posters (no names mentioned) have even posted one answer one year and reversed course in later years. Some say inject before the SWCG to prevent scale build up. Others say never to do that and put it after so you don't shorten the life of the salt cell. The Pentair IntellipH system, I believe, recommends before (between the heater and the SWCG, for example). Hayward instructions don't indicate anything. I'm favoring after since I can put it after a FloViz that is plumbed in just before the returns leave the pad. This would serve as a check valve in case of accidental overdose.

What is the current consensus for acid injection site?

(BTW, if you're wondering, my plaster is about a year old, but I get enough aeration for a steady pH rise despite low normal (50-60) TA. Tired of slowly pouring in the jugs of acid.)

Thank you.

 

[Rattus Suffocatus]

I typically descale my cell with 8:1 water to acid (though the manufacturer says 3:1 in one place and 4:1 in another)... so, if you did that and put it upstream from the cell, you'd be continuously descaling.. that probably would shorten the life of the cell, honestly. If you put it downstream it will get buffered through the entire volume of the pool (or at least in theory.) If it keeps your CSI and numbers in the proper balance I couldn't see how that wouldn't logically be the perfect solution. Now.. if you are like me and tend to have terrible TA all the time, maybe additional acid before the cell would be okay.. but how much? I'd argue 8:1 would be too much. But your TA is good..

I think the issue with putting before the cell is "how do you know that you aren't hurting the cell?" I don't know how you would know or even figure that out as a cause if you had an early failure.
After? Well if the water is as good as it gets, it's as good as it gets. Right? That's my thought experiment for the day, I suppose.

 

[Newdude]

see the opinions over the years have varied. Some frequent posters (no names mentioned) have even posted one answer one year and reversed course in later years

Ha !!! Just goes to show you though that we strive to have the discussions here and opinions can be swayed with good reasoning presented by others.

Hang tight for opinions. I don’t stand a chance here seeing how you short circuited poor Fred above. I’m not even gonna try

 

[santacruzpool]

I use diluted 14% acid (final % is around 7%), and the injection rate is so slow that I think the water that is passing through my SWCG is just slightly more acidic - I tested at the nearest return and it was around 6.8 PH.

I also turn up my RPM to 2000 from 1000 for 1 minute to keep the water flowing by the plates at a faster clip - and the 2" pipe holds a lot of water honestly. I can't imagine that there would be any effect on the plates at all. I tend to need to lightly acid clean my cell every year anyway. My water parameters, despite good TFP numbers, still tend to lead to a bit of scaling, and I always get a little build up around the pins and a tiny bit of scale on the edge of the plates. I still had to do a quick acid cleaning after the first year of using my pump, so I don't think it is helping, or hindering scale buildup in my situation.

 

[CaptainCannonball]

I appreciate the OP for asking the question. I have a upstream Stenner setup leftover after my conversion to SWG and thought about using it for acid. With water flowing at 25 gpm and the Stenner trickling diluted acid it is kind of like someone peeing in a river a mile upstream, can’t imagine you would still taste it.

 

[TexEdmond]

Just curious, do you fight rising alkalinity from high TA fill water as well? If you're able to keep your TA in the 50-60 range and are concerned about SCG longevity, you might consider adding borates? Several members here say they've done that and barely touch the acid jug anymore. Either way I'm curious to hear as well, as I may have to install an acid injecter someday as well given my fill water situation.

 

[e_sully]

Great replies so far. Thanks @Rattus Suffocatus, @santacruzpool, and @CaptainCannonball for your thoughts. It does sound like it probably makes no difference whether it is before or after the SWCG. I'm still leaning towards after the SWCG since I have a check valve there in case of an accidental acid dump.

@TexEdmond, I do have borates. My TA does creep up from the fill water, but not too quickly. My undertanding is that borate doesn't decrease your acid requirement, just how frequently you add it. Honestly, it hasn't made much impact on my acid need, but I subjectively feel the water is just a tiny bit clearer. I used boric acid from Duda Diesel, so it was trivial to add. Maybe it helps kill the bugs that land in the water.

 

[Rattus Suffocatus]

I really ought to add borates, but until I put a fence up around the pool, I can't keep the dogs out of it, and I rather not risk even slight amounts of toxicity to them. But since I have one that can't seem to leave the pool or the solar cover alone, I suspect that if I don't move first, a fence is coming next year early in the year. When that happens, I'll do a small amount of borates. A move is possible, unfortunately.

But in the mean time I try to dose acid at least 3x a week, 2x if I am extra busy. I have a peristaltic pump that I was goin got use for acid injection.. I really ought to revive that project before next season.

And as far as upstream versus downstream... if I were to put it upstream, I might do it in front of the filter and then I would agree that the 50+ gallons of water in there probably would dilute it enough to be okay. My situation with TA is so bad I have to sweep up white flakes ever week. I guess in my case the acid might be less of a problem than the calcium flakes...

 

[TexEdmond]

Given the choice of usernames, it makes sense you'd be concerned about animal life around the pool. . Good on you for putting their safety first. We're fortunate our dog is a complete princess who doesn't want to walk on wet grass to pee, much less get closer than 18" from the pool coping if she can manage.

I've shoved my pH down and aerated a few times in the last 6 weeks. TA went from 200 to 70 and along the way I was doing some dumb stuff like using up my stash of Cal-Hypo that was making it harder. I've put (EDIT for bad arithmetic) 17 gallons of MA in my pool since the middle of June, but that's tapered off now that TA has plateaued... This last pH / TA shove I did only brought me back to 70 from a refill of a few hundred gallons that raised me to 80. Even though my CH has risen in that time, I don't have calcium snow on the pool floor anymore like I did starting out.

What's your maintenance level of TA now? Do you think the pre-filter injection would run the risk of solidifying oils not yet washed out of your filter?

 

[Flying Tivo]

Im 3 years in with my acid stenner with Pre SWG injection. Decided long ago to leave it like that. I concur with the dilution idea. What i did different is that dosing should not coincide with the SWG calibration as it throws off readings, not by much, but it does. I have high Fill TA 250 and like Ph around 7.4 for confort on the eyes. So its a win/win.

 

[Rattus Suffocatus]

I try to keep TA under 100 but struggle. And yeah, it should be much less. I don't have a heater so I can keep the pH a little lower to lower the CSI, but it still flakes from the TA. I have had flakes like crazy this year because I've not been able to keep up with the pool. I am almost tempted to pay someone to vacuum/sweep the thing up, but other than that the water is in good shape. We haven't used the pool much due to a string of disasters (I can't use the pool or hot tub myself temporarily due to a medical problem) and it really needs a good sweeping, filter cleaning, etc. Hopefully it will stop raining this weekend and I'll have time. The fill water hits TA 180 here in the summer. There are more rocks in the water than water here, it seems. But especially from the second story window, the bottom of the pool is pretty dirty. Lots of storms blowing dirt in this year and the dogs don't help either.

I somehow ended up with 4 dogs, 3 cats and two birds. One dog almost got into a Colorado river toad this morning, but I think we caught her in time-- made me late for work though. All my heathen dogs will drink out of the pool if I am not correcting them.. one loves to swim (the male Golden Retriever)-- hard to keep him out-- he likes to eat the solar cover as well, one can swim well but doesn't (the old Labrador).. and the other two are too prissy to swim. (Springer Spaniel who almost got the toad and an Australian Shepard who won't even go out in the rain!) The Shepard was a pet sitting gig that my daughter did and the family had to move out unexpectedly, so guess what?!?... she's a PITA.... too "smart" for her own good. The golden was a gift from my wife to replace the old Lab because she is getting really old.. but has outlived her expected life so far by over a year. Unfortunately, he's not getting the attention he should. Hopefully I'll get to train him before he's too old... we will see... loves people....

But yeah, everything here in Arizona is trying to kill them like the toads. I don't want to speed up the process with making the pool water toxic.

The birds are easy.. the cats all have their favorite person in the family and are easy (and pretend to hate each other)... the female tabby is my buddy. I saved her when getting torn up on the farm in Iowa as a kitten (she was a bad$$$ hunter) and unlike my kids, she's grateful....Took to inside life and never looked back....

But yeah, I live in a literal zoo, but mainly because of my teenaged and young adult children....

The drowned rat, by the way ... is me....

 

[TexEdmond]

This is from the Pentair IntellipH manual. "In between heater and SWG," says them.

 

[Flying Tivo]

Now i know why i installed it that way!
I always read the instructions, but forget them quite easily.

 

[TexEdmond]

I always read the instructions, but forget them quite easily.

I almost always put together the SECOND Ikea bookshelf upside down and backwards...

"This was so simple. I don't need these instructions!"

... A few minutes later ...

"RATS! WHERE ARE THOSE INSTRUCTIONS?!"