Homemade Acid OR Chlorine Injection System

[mas985]

Having a plaster pool with a SWG and fill water with high PH and TA has meant a constant battle with rising PH. I have tried the borax route with lowered TA but because of the high TA fill water, I haven't had much success in lowering my acid use. So I decided to look into acid injection systems. HASA has one but it requires the liquidator and you are only suppose to use dry acid with it. A peristaltic pump was certainly one option but before I spent the money for that, I thought I would try making my own.

This concept can be used for chlorine as well but do not mix acid with the chlorine.

The concept I am presenting here uses the suction created by the pool pump to slowly draw a water:acid (or chlorine) solution from a supply tank. When designing this, I wanted to make sure I could control both the flow rate of the solution as well as the dilution ratio entering the plumbing system. Because the solution is entering at the pump, it is very important that the resulting mix is significantly diluted so as not to lower the PH or TA enough to cause damage to any of the equipment (i.e. corrosive water). Please do not attempt this unless you are comfortable with some DIY experimentation and willing to tinker with the dilution to make sure you get it right.

Warnings:

This setup should only be used on those pools that have chronicly high PH and predictable acid dosing. There is a chance of overdosing the pool with acid so it is best used on those pools that experience rising PH. Ignore this for chlorine injection.

If you have an above ground pool or an inground pool that is much higher than the pad, a check valve will probably be required to prevent backflow. An all plastic aquarium valve can be used or something like this. Also, with these same conditions, you may find that the tank needs to be elevated such that there is positive flow from the tank to the pump. If you remove the drain plug from the pump's suction side and water squirts out instead of air being sucked in, the tank will likely have to be elevated.

If you have an attached spa, be aware that the PH may drop too much during a spa run since turnover in the spa is much shorter than turnover in a pool. One solution to this problem is to inject the acid into the pool suction pipe instead of the pump so no acid is drawn when in spa mode. However, this means that a hole needs to be drilled into the plumbing.



SETUP DESCRIPTION

The setup is quite simple and most of the components are available at Walmart and/or Home Depot. I will have pictures at the end which shows the parts and how they are put together. Here is a list of parts:

Large tank - the larger the better. Home Depot bucket with a lid is a cheap option. You can even use several buckets with tees to tie them together.

10' x 1/4" clear vinyl tubing or black irrigation drip tubing - I like the clear tube because you can see the fluid moving but it isn't UV resistant.

2-10 1/2 GPH drip irrigation buttons. Lower drip rate would be better but harder to find. These are used to control the flow rate which is proportional to the pressure drop across each one. Instead of drip buttons, you could also use a polypropylene needle valve such as this.

1/4" hose to thread plastic adapter for pump drain plug - ice maker parts work well for this and I found mine at Home Depot

1/4" hose valve - nice to have in order to shut off the acid flow but not really necessary

3/16" check valve - required for pads below the pool water surface. An all plastic aquarium valve can be used or something like this.

The first step was to create several drip assemblies. You might start with 4 to see how the flow rate is and go up from there. I use 1 1/4" of 1/4" black irrigation tubing on the barbed end of the button. I also hot glue this end since it tends to leak air a little. The other end will not be glued so that multiple buttons can easily be added or removed as needed to control the flow rate. Plumbers grease is good to have an air tight fit when pushing the hose onto to the smooth end of the button. The rest is pretty easy and just requires the fitting in the suction side of the pump and the hose in the tank as shown in the pictures.

The next step is to target the desired minimum period between refills of the tank. Larger tanks will allow for longer refill periods so choose accordingly. When setting up my draw rate from the tank, I targeted a minimum of 2 weeks between refill of the tank. Because I use only 1/2 gallon of acid a week, I could have easily targeted 4 weeks for refill but you will have to decide what works best for you.

Another factor is how much acid is used within the refill period. Most pools will use less than a gallon a week so this should not be an issue. Even two gallons a week with a two week refill period results in 4 gallons of acid or close to 1:1 water to acid in an 7.5 gallon tank which is a little high but doable. If your pool needs that much acid, I would suggest a 1 week refill period or larger tank so the tank dilution can be closer to 2:1.

Chlorine will also benefit some from dilution since it tends to degrade slower.

Once you have a targeted draw rate you can then work out how many drip buttons you will need. The draw rate from the tank is also dependent on the amount of suction from the pump so it is best to start out with the worst case or highest suction. This tends to be the lowest PSI reading on the filter. So you want the lowest head loss on the return side (e.g. no solar) and the highest head loss on the suction side (e.g. suction cleaner engaged). With a 2 speed pump, calibration is probably better done on high speed since low speed will have a higher dilution ratio.

The opposite is true for chlorine since the residual chlorine must be kept at a minimum level. So set the plumbing for the highest return head loss and the lowest suction head loss. This will make the draw rate a minimum and easier to set the minimum chlorine level.

Based upon the desired draw rate and pump run time, you can determine what the draw rate is in oz/min. For example, my pump runs 6 hours per day and I have a desired draw rate of 7 gallons in 2 weeks. So the instantaneous draw rate is .18 oz/min so the optimum draw rate would drain 1 oz of fluid in 5.6 minutes. With a measuring cup and timer, you can fine tune the draw rate with the drip buttons. Go for a slightly longer draw rate so that you will get at least the minimum refill period.

By setting up the draw rate and the amount of acid used within the refill period, you are assured that the dilution ratio will be high enough. However as a double check, it is good to do the math to verify this. Unfortunately, you need an estimate of the flow rate in your plumbing. A low estimate is best so you can simply use a head value of 4*filter PSI and look up the flow rate on your pump's head curve. This should be on the low side. The dilution ratio can then be estimated from:

Dilution ratio = Pump GPM / Tank GPM * Tank Dilution

For example, I know my pump runs at about 88 GPM. If the draw rate on the tank is 7 Gallons in 2 weeks and I run the pump 6 hours per day, the target draw rate from the tank is:

7 Gallons / (14 days * 6 hours/day * 60 minutes/hour) = .0014 GPM

Since I use 1 gallon of acid for 6 gallons of water in the tank, the dilution ratio is then 88 / .0014 * 6 = 377,000:1 which is more than enough dilution. The often sited acid mixture of no more than 1 pint per 10,000 gallons of water is a dilution ratio of 80,000:1. I can halve the tank dilution and draw rates so I can fill the tank every four weeks and have the same results. So there is a lot of flexibility built into this system to meet the needs of any pool owner.

The final test is to verify the PH and TA of the water coming out of the plumbing which can be done by capturing water from a return. Let the pump run for a while to make sure the lines are purged of air and the water:acid mixture is actually entering the plumbing system. I run my pool in spa spillover for a couple of hours and measure the spa PH and TA for verification.

The same procedure can be done for measuring the chlorine level coming out of the return.

Also, if you turn off the pump each day, it is a good idea to check the pump basket PH (and chlorine) before the next run cycle. This can determine if you are getting any flow while the pump is off and if it is enough to cause a problem.

If you find that the tank is not draining completely within the refill period, this is OK. Just add the normal amount of acid and top off with water (remember to have at least 1/2 tank of water before adding acid). As long as you are adding the correct amount of acid per refill period, the dilution ratios will work out ok (lower draw rate allows for lower dilution). Weekly testing is still recommended and every other day when first starting to use it.

If you find that the tank is draining sooner than you would like then add additional drip buttons.

As a final note, I have been running my system for two months now with fairly constant PH levels but the real test will be this summer when PH rises faster and pump run times are longer. It is a good idea to keep a close watch on PH levels when changing the pump run time since this adds more acid but PH usually rises faster too.

Hopefully this is enough detail to get you started.


On to the pictures.

Drip button with 1 1/4" of 1/4" drip hose

Multiple drip buttons together

Fitting in pump suction drain plug with hose

Hose, buttons and tank

 

[smuggs]

am i missing something, or could a similar set up be used as a "homemade liquidator"?

 

[mas985]

There might be an issue with smell and degradation of chlorine. The liquidator puts a layer of water over the chlorine to contain the smell and help reduce the loss of chlorine. This setup would not have that advantage.

Other than that I don't see why it wouldn't work for chlorine as well although less dilution may be required because more chlorine than acid is needed. I don't think the low PH would be an issue since again the draw rate would still be low enough so as not to cause an issue. Just don't mix the chlorine with the acid as there could be a serious reaction.

Running some numbers:

With 6% chlorine, 21,000g pool and adding 1 ppm per day you would need approximately 44 oz per day or 5 gallons in two weeks. So a slight dilution is possible for the same two week refill period as the acid. This would help with the smell and degradation issue. A larger tank would help as well so the solution could be diluted more.

 

[smuggs]

I haven't found myself having much of a PH issue, although the pool was just built last year, so I wouldn't see myself needing an acid injector. In any event, the pool does currently have a tri-chlor puck chlorinator, which I used last year. The only time there was a odor issue then was when I opened up the container. I think I may look into this as I intend to use BBB this year, but will not be able to be on top of the chlorine levels myself on a daily basis due to my work and travel schedule. I intend to teach my wife, but with 3 kids, including a now 5 month old, I'm sure it will be challenging.


anyway....can't wait for pool season up here....but still hanging on for a couple more days of skiing up in VT.

 

[Aquaman95]

Mas,

You've done a real nice job with that.

 

[mas985]

Mas,

You've done a real nice job with that.

Thanks. Much appreciated.

Hopefully it will be a decent long term solution.

 

[duraleigh]

Mark,

If you have a check valve in the system, I don't see it. When the pump is off, that should result in positive pressure in the pump basket causing a backflow into the container. Am I missing it?

 

[mas985]

Dave,

I have solar so there is a check valve right after the filter not shown in the photos.

Even without a check valve, I think the back flow would be much smaller than the forward flow since pressure at the drain plug is pretty small with the pump off.

However, even with some backwards migration, this set up tends to be self correcting over time as long as the backwards flow is much less than the forward flow. If you continue to add acid to the tank at a rate that you would normally do manually, then over time, the dilution ratio will adjust to the "average" draw rate from the tank such that it should be adding the required acid during the run time. So if I add a gallon of acid every two weeks and the tank is empty at two weeks, then I have added a gallon of acid over those two weeks. It doesn't really matter if water flowed backwards unless it is more than the forward flow when the pump is on.

 

[duraleigh]

Mark,

I have been working on a chlorinator using the same principles. It never crossed my mind to use it as in acid inducer for which it seems much more suited. I really like the concept and, while it can be adjusted to a chlorinator, it doesn't work very well because of the different volumes involved. A check valve is almost a requirement and. most importantly, the valve has to be truly microscopic to make the whole thing make sense and that's the big draw-back.

Another thing I have deteremined is that it won't work on AG pools because the pump basket is under constant positive pressure.....even with the pump on.

That said, I really like the idea as an acid inducer and perhaps what you have learned can help develop a chlorinator based on the same principle. "The Liquidator" is great but it is, IMO, more complicated than it needs to be. Aside from the AG Pool restriction, the only snag I kept hitting was a valve that would meter 12% chlorine in small enough doses to make the apparatus really convenient.....i.e. small enough that you could run without refilling for two weeks based on an 8-hour pump run-time daily. I never saw the chlorine "smell" as a restriction because so little of the jug is exposed to the atmosphere (just enough to break the vacuum as it pulls chloprine from the jug)

 

[austinnichols101]

Mark,

I have been working on a chlorinator using the same principles..."The Liquidator" is great but it is, IMO, more complicated than it needs to be.

I've had my liquidator for about three weeks now and every time I walk past it I get the itch to work on some improvements. With a simple swap and an extention to the drop tube and I could have my own 32 gallon Liquidator HD. I would really like to have more space between the inlet opening and the top of the liquidator so that I could add a 2.5 jug of chlorine in one continuous pour (instead of waiting between pours).

 

[mas985]

Mark,

I have been working on a chlorinator using the same principles. It never crossed my mind to use it as in acid inducer for which it seems much more suited. I really like the concept and, while it can be adjusted to a chlorinator, it doesn't work very well because of the different volumes involved. A check valve is almost a requirement and. most importantly, the valve has to be truly microscopic to make the whole thing make sense and that's the big draw-back.

Another thing I have deteremined is that it won't work on AG pools because the pump basket is under constant positive pressure.....even with the pump on.

That said, I really like the idea as an acid inducer and perhaps what you have learned can help develop a chlorinator based on the same principle. "The Liquidator" is great but it is, IMO, more complicated than it needs to be. Aside from the AG Pool restriction, the only snag I kept hitting was a valve that would meter 12% chlorine in small enough doses to make the apparatus really convenient.....i.e. small enough that you could run without refilling for two weeks based on an 8-hour pump run-time daily. I never saw the chlorine "smell" as a restriction because so little of the jug is exposed to the atmosphere (just enough to break the vacuum as it pulls chloprine from the jug)

You are correct in that AG pools and even IG with pads well below water level would potentially have problems with this setup. The positive pressure at the pump basket would force water back into the tank.

Although there will be pool setups where this concept would simply not work, as long as you have a net postive water flow out of the tank over a 24 hr period, it shouldn't matter too much. Even AG pools could have negative pressure at the pump basket with the pump on but the head loss in the suction plumbing would probably have to be more than twice the height of the pool to come out ahead. An easy test is to unscrew the drain plug in the pump with it on and see if air is drawn in or water squirts out.

The real key to this concept is the flow control. Industrial metering valves would allow for fine control of the flow but would be very expensive. I went through several proof of concepts before settling on the drip button. I cut one open and found a zig zag pattern for the flow channel and realized that the button should work for flow control even for low PSI values. These devices have flow rates which are proportional to the PSI drop over the button. So the more buttons you add, the slower the flow rate and there really is no practical limit.

However the range of suction at the pump can be quite large. With my suction cleaner engaged and no solar, I have close to -6 PSI at the pump basket. Without the cleaner and solar engaged, the PSI at the pump is -2.5 PSI or 60% less. This means that the flow rate will change at the extremes by 40%. So this does need to be taken into account but in a typical 2 week period, it will average to an acceptable draw rate but may fluctuate week to week. I don't this this should be a problem given the range of acceptable PH levels. Chlorine levels can fluctuate some as well without becoming a problem.

During the winter, I run my pump 2 hours per day with the cleaner going most of the time so my draw rate is quite high. Still with 6 buttons and only 2 hours pump time per day, the refill period is 4 weeks. I only need 1 gallon of acid in this 4 week period so it works out just fine.

This summer, I am expecting 6 hours of pump run time and using solar most of the time. I expect that the draw rate will decrease by 40% but the run time is 3x longer therefore the refill period should be about 2 weeks. Last year I used about 1/2 gallon of acid per week in the summer so in 2 weeks this will be 1 gallon which will be perfect. So I think I will be able to get away with the same button count during the summer. This may not work out as well for some people but I think most will be able to find a steady state which works well with their schedule and allows them to add X gallons of acid every Y weeks. It just requires some experience and tinkering to find out what works.

Also, I still think that it should work fine as a chlorinator as well since the flow rates and dilution can be easily adjusted. However, it may required larger tanks to accomplish. Even if you need 1 gallon of chlorine per day, theoretically, you can use the same 7.5 gallon tank and set the refill period to be one week. I don't think most pools require that much chlorine so some dilution in the tank or longer refill periods will be possible.

What makes products like the liquidator very useful is that setup is much easier than what I am proposing. Also a Peristaltic pump makes flow adjustment even easier and you can inject the acid into any portion of the plumbing system. However, those pool owners who are not affraid of a little experimentation my still find this an acceptable and very cost effective solution.

 

[mas985]

Mark,

I have been working on a chlorinator using the same principles..."The Liquidator" is great but it is, IMO, more complicated than it needs to be.

I've had my liquidator for about three weeks now and every time I walk past it I get the itch to work on some improvements. With a simple swap and an extention to the drop tube and I could have my own 32 gallon Liquidator HD. I would really like to have more space between the inlet opening and the top of the liquidator so that I could add a 2.5 jug of chlorine in one continuous pour (instead of waiting between pours).

These tanks would be a bit safer than an garbage can but you can use one. I started out with a 5 gallon paint bucket but I really wanted something that I could seal well and would not be too easy to spill or get into.

 

[mas985]

I updated the procedure to include instructions for using this as a chlorine injection system. The concept and implementation are similar and about the only difference is in calibration and setting the minimum chlorine level.

 

[matj6876]

Mas,

This is just what I have been looking for.
I was concerned that a year after new plaster I am still adding just over half a gallon of acid a week to my 15,000 gal pool.

I am a bit of a noob at this type of stuff and had a few questions for you before I kicked this off:

I have a spa and historically have run it for 1 hour a day, just to turn it over. Is there anything proactive I can do to avoid excessively low pH here or is it just a case of suck it and see?
Your Math secretly terrifies me! Is there any problem in setting this up completely by trial and error (using water only of course) until I get a flow rate of somewhere around 4 gal/week and then using a 3.5:1 mix of water and acid at that stage? This would give me my 0.5 gal/week of acid right?
If during this trial and error stage, or even at some point after it, the tank runs dry and the pump starts drawing in air…. How bad is that?
I assume that freeze protection just screws this up completely? Right now I am running my pump 42 hrs/week but Freeze protection can easily double that and more. I’m guessing that when it’s that cold you turn the valve off and go back to adding acid manually?

Thanks for the idea and detailed instructions. Cheers!

 

[mas985]

Mas,

This is just what I have been looking for.
I was concerned that a year after new plaster I am still adding just over half a gallon of acid a week to my 15,000 gal pool.

I am a bit of a noob at this type of stuff and had a few questions for you before I kicked this off:

I have a spa and historically have run it for 1 hour a day, just to turn it over. Is there anything proactive I can do to avoid excessively low pH here or is it just a case of suck it and see?

I have found for my spa that I can run for about an hour and have a 0.4 PH drop or 7.6 to 7.2. Additional running will lower it further and probably get into the danger zone. However, if you are running the jets at the same time then the PH drop will be much less due to the aeration and may not drop at all. There are too many variables involved to predict what will happen. The first time you use the spa with the acid you should probably test the PH every 30 min or so until you get a feel for how fast the PH is dropping.

So yes it is a bit of trial and error which is why I suggest not using the dosing during spa use. A small valve like I show in the picture will allow you to turn it off during spa use. But that may not be practical if you are running every day.

Your Math secretly terrifies me! Is there any problem in setting this up completely by trial and error (using water only of course) until I get a flow rate of somewhere around 4 gal/week and then using a 3.5:1 mix of water and acid at that stage? This would give me my 0.5 gal/week of acid right?

So if you are drawing 4 gal/week and you want 0.5 gallons acid in that same week then the ratio is 3.5:0.5 or 7:1.

If during this trial and error stage, or even at some point after it, the tank runs dry and the pump starts drawing in air…. How bad is that?

I have tried this and it sucks very little air and not much happens at all. Eventually, the air may accumulate in the filter but this should not be a problem and when you fill the tank again, you can bleed the air from the filter.

I assume that freeze protection just screws this up completely? Right now I am running my pump 42 hrs/week but Freeze protection can easily double that and more. I’m guessing that when it’s that cold you turn the valve off and go back to adding acid manually?

Yes freeze protection means more pump run time so more acid in the pool. One question though is are you really sure that you need freeze protection. I say this because I am in an area which sometimes goes below freezing but I don't really need freeze protection. The equipment pad has a lot of latent heat so it takes a lot of time below freezing to actually freeze the water in the plumbing. If you have freezing temps for more than 8 hours then you probably do need freeze protection, otherwise you may not. One test that is useful, is to put a shallow dish of water (2" deep) on the pad next to the equipment and see if freezes solid. If not, you probably don't really need freeze protection.

Another option is to change the dilution ratio during the period of time that you have more run time. This is usually somewhat predictable at certain times of the year.

Thanks for the idea and detailed instructions. Cheers!

One other thing you need to check is the pool water height in relation to the tank height to make sure you will not have forward or backward siphoning when the pump is off. This can throw things off as well. Forward siphoning can mean accumulation of acid in the pump basket while the pump is off. The PH can drop and there will be short period of time with low PH through the plumbing. Not too serious but could have implications over time especially if you have a heater. Backward flow is not too bad since it is diluting the mixture further but it may make it more difficult to setup.

Ideally, it is much better to use a peristaltic pump but these can be expensive and prone to failure which drove me to this solution. So just be careful when setting this up and double check to make sure you are not introducing too much acid.

[EDIT] Another solution for those with spas is to inject the acid in the pool suction pipe. This way, when in spa mode, no acid will be sucked in. However, this does mean you need to drill a hole into the plumbing.

 

[matj6876]

Mas, Thanks for the quick response.

SPA - OK will run with the trial and error and if I have too many issues will drill in to the pool suction pipe. Let's see.
MATH - See I got that wrong already. My bad. Will work on this!
AIR - OK. Good with that.
FREEZE PROTECTION - I have always thought that having all pumps running when the air temp drops below 37F is a bit excessive but I don't know how to change it. I have not studied my pentair manual too hard. One for another thread?

I stopped by Home Depot on the way home and have kicked this off:

As my math is sooooo bad I decided to just put the bucket there and see if it sucked water in when the pump ran. It does! :lol: It's now standing to see if when the pump is not running I get a load of back flow.

Question: In the picture what is the second plug in the pump for (noticed you had one too)?

 

[mas985]

The second plug is the pressure side drain plug. This is the high pressure side of the pump.

As a side note, I am currently working on another solution which uses the pressure side plug instead of the suction side. Albeit that it is a more complicated setup, this setup will use the pressure of the pump to suck up the acid solution via a modified garden sprayer (the kind that fits the end of a hose) and deliver it to a return pipe further along the plumbing after the heater. This alleviate all of the concerns about putting acid in the pump. But the downside is that the return side plumbing will have to be drilled into. Just another option if the suction side does not work out.

 

[lovingHDTV]

I'm quite interested in this setup as my pool also consumes ~1/2 gallon of acid per week and I have borates in it also.

The one issue I see with my setup is that the pump/pad is ~8 feet below the pool water level. Would a simple check valve in the line pre/post the drip heads fix this?

EDIT: As a follow up, I did run my pump on low, removed the plug and do get air sucking into the pump. So that part will work. So it looks like adding a check valve should allow this to work.

thanks,

 

[mas985]

I'm quite interested in this setup as my pool also consumes ~1/2 gallon of acid per week and I have borates in it also.

The one issue I see with my setup is that the pump/pad is ~8 feet below the pool water level. Would a simple check valve in the line pre/post the drip heads fix this?

EDIT: As a follow up, I did run my pump on low, removed the plug and do get air sucking into the pump. So that part will work. So it looks like adding a check valve should allow this to work.

thanks,

I am acutally surprised that you have suction at the pump with it being so low. Having the pad below water level is actually a better setup since that prevents flow while the pump is off. A check valve should work ok just make sure it doesn't have any metal in it. I think that aquarium stores have small check valves for tubing but I haven't tried those yet.

 

[matj6876]

Re: Homemade Acid or Chlorine Injection System

If the tank is significantly above the pool water, siphoning may occur drawing the acid solution while the pump is off and droping the PH too much in the pump basket. So I would suggest not using this setup if the tank bottom is more than a foot above water level.

If I make the assumption that my house foundation is still level then I think the base of the bucket is about 4" above water level. However, after about a week of messing around it looks like I fall foul of this "warning".

All the tests I have done so far have been without drip buttons in place. I fixed all the leaks and when the pump runs it draws about 5 Gal/hour through a wide open 1/4" OD pipe. When I turn the pump off .... I still lose about 0.5gal/hour into the pump.

Is it worth me trying to calibrate with drip buttons? They will obviously limit the loss when the pump is not running but can they eliminate it? Possibly not the solution for me

Here's to waiting for the pressure side solution!