Acid Injection

[jerryk1234]

Hello,

In the Fall, a young man's fancy turns to pool equipment...
I am really getting tired of constantly dosing this pool with acid. Am considering an injection system. I would prefer it to be an "open loop" deal where I monitor the PH myself and adjust the amount of feed accordingly....because I do not trust PH sensors. I have two handheld PH meters - a cheap one and a more expensive one - and they both require babysitting and hand holding to work.

Starting the search - I see Hayward makes one and Pentair makes one. Stenner also makes one - and I think they make the actual pumps for everybody else.

Pentair's unit seems to be intelligent - and it requires intelligent connections to a larger Pentair system.

Hayward's acid injector OTOH is stupid. I like stupid. It has a power cord. As long as the power cord is powered, it pumps.

I would need some sort of very simple controller to pulse the output to the pump. With, say, a knob marked 0-100. At "50" it would
let the pump run for say 5 minutes, and then leave it off for 5 minutes. That would be simple enough to do with a 555 timer chip driving
a 110V relay. Or I could get fancy and use a small microprocessor.

This is starting to seem a little urgent because my CH has risen to 500, and I need to control the PH more tightly or risk scaling, at least until I get up the gumption to do a partial water change.

 

[ajw22]

Homemade Acid OR Chlorine Injection System

Mark, sorry, I may have my terminology all screwed up....how can I tell the suction side from the pressure side, realizing I need to use the suction side? Also, I have been thinking about this, and is there any reason a brass needle valve would not work? I was also thinking of solving the...

www.troublefreepool.com

 

[mguzzy]

Sounds like a fun project.. to occupy a young man's fancy through the cold wintry months, but...

What the heck is going on in your Pool that requires constant injections of acid every 5 minutes! wow. (I know you were using that as an example)

 

[santacruzpool]

I installed a Pentair Acid Pump & Tank and hooked it up to my Jandy automation panel last spring.

It is not a smart pump, but since I hooked it up to my Jandy automation I can schedule acid injection and/or do the injection manually via my Jandy Zodiac iAqualink online and phone based app. I can set it to run for 1 minute which puts in around 4-5oz of acid into the pool - at the same time I turn up the speed of my pump to help disperse the acid a little more...

You could also hook it up to a standard 24V DC power supply and add a timer and a manual switch to control it.

 

[AUSpool]

I would ask first, what are your numbers and if you had a TA of ~70ppm where would your pH settle at? I do realise that in CA you may have an elevated CH but if you can low your CH, let your pH balance and manage your CSI via TA adjustment you wont need an acid dosing system.

 

[AUSpool]

...
This is starting to seem a little urgent because my CH has risen to 500, and I need to control the PH more tightly or risk scaling, at least until I get up the gumption to do a partial water change.

Sorry I missed this and should have used it in my post above. I good starting point is to test your fill water for CH, TA and pH. Plug your numbers into poolmath and play with some scenarios, winter is coming and with your water temp dropping your CSI will decrease, too giving you a bit of breathing space. If you let your pH run a little high you will prevent your CSI from going too low and also get a good idea where your pH will stabilise at.

I’m thinking of an acid dosing pump for the start up of a new pebble pool. I too like simple, power on, pump runs. I can test my pH, work out the dose required and set a timer to deliver the required amount when the main pump is running. Maybe get real fancy and run the dosing pump twice a day. But hopefully I’ll only need it during the start up so I’ll probably just go manual and avoid the extra equipment and cost. In your case, once you know your top up water numbers, you may be better off doing a water change and/or investing in a water softener to reduce the CH in your tap water.

 

[jerryk1234]

My example of XX every five minutes was a number I pulled out of my ear. Really, what's required is about 8 ounces a day. The technique of regulating amount of something by pulse width is called "PWM" ( Pulse Width Modulation ). Most PWM - say for motor control - is relatively fast, from 1000 to 20000 pulses per second. What we want is to have the pump run full blast for a while, and then turn off. One could sort of almost do it with one of those rotating clocks with push-tabs all around their circumference. The trouble is - control would be very rough, in increments of 15 minutes. Actually, now that I think of it, PWM is probably not appropriate. There's just not enough flow. Probably a "run this many seconds per day" arrangement would be better.

That suggests a microprocessor. I have a couple of "nodemcu" cards in my junk. These have an ESP8266 processor,
a modicum of rom & ram, built-in wifi, and enough I/O to do the job.

Another requirement is that the system ONLY run when the pool filter is circulating.

 

[jerryk1234]

Our tap water CH around here is about 25 ppm. It's nice water. In fact, when the pool builder started the pool, he had to add calcium. My notes show that on 11/17/2018, the CH was 175. I added calcium chloride to get it up to 275, and never added any more. I can only guess that calcium leached out of the new plaster.

The PH doesn't really stabilize. It just keeps getting more and more alkaline. I think that's because of the salt system.

 

[jerryk1234]

Another thing I have is a fancy open-source irrigation controller running my drip system. I could run a line from that controller to a relay controlling the acid injector and program it to run - once a day - as many minutes as are necessary.

 

[bdavis466]

Another thing I have is a fancy open-source irrigation controller running my drip system. I could run a line from that controller to a relay controlling the acid injector and program it to run - once a day - as many minutes as are necessary.

That's probably the simplest way and pretty reliable too.

 

[Costas > DownUnder]

One other thing to think about is what sort of tubing will be suitable for the acid.

Most flexible tubing does not last long.

What I found is best (by far) is EPDM type tubing - This can withstand HCL at 32% strength if needed.

With a diluted lower strength mix it will last for years.

Trick is to find some at a suitable ID. Here in Australia I ended up purchasing some tubing which is designed for PC water-cooling applications (one of my side hobbies) Search results for: 'zmt' – EK Webshop

You can also purchase this product in the US LINK but you may even find something even more suitable as far as the ID/OD dimensions are concerned.

 

[mrwoo]

I would go with an LMI pump if it were me. Rock solid, variable pump stroke, great chemical compatibility, and the ability to run off a pwm signal. I used to use 93% sulfuric I diluted (very cautiously) to 30% but now pump straight 50% food grade from a drum. I use a seasonic controller which monitors an inline paddle wheel flow meter and this sends a pwm to the LMI pumps. It's a fantastic although spendy system. This is for horticulture, but the application is the same, you treat your water with a chemical via a pump.

I use Cole Parmer probes along with "eutech" controllers which have relays as well as V/PWM outputs. I have both pH and conductivity on those and used to program a little unit to monitor and log in a server. Regardless, the cole parmer branded probes and meters/controllers I've used in the past 12 or so years are all still working, and this is commercial 24/7/365 application. Probes of course need to be taken care of and replaced periodically, but you get my point.

I would not use a dosing pump that is water driven. I've tried all of them, and none of them are reliable any longer. I have a patent pending on an injector for fertilizer that is accurate but not a water driven "motor" style. I've seen a 3% acid solution turn some of these plastic injectors to dust, the "mixing chamber" almost always has metal parts (a big no no) and in the last 5 years, they are buying cheaper parts because they will begin to seize after X number of hours use. As I've used them and also been a dealer and repair center for one brand in particular, I can tell you after 34 years that if your flow rates and solution concentration are within the bounds of an LMI pump head, you will not be disappointed.

 

[mrwoo]

Also if you do decide to inject there is a product called a static mixer that helps to get the injected solution mixed immediately upon injection. May not matter once pool pumps circulate but it might matter for the plumbing. Even sulfuric acid which loves to mix with water can stay in a small area inside a piped system. It can come out in streaks and also pool up and cause damage.

Just an FYI.