Acid injection, Chlorine injection and SWCG

[diverminh]

Hello,

My pool is currently in the process of getting remodeled. The plumber/electrician has completed setting up my equipment. As you can see from the picture below, I have a SWCG right after the pump. Then it makes a few sharp turns before it heads back to the pool. I had the plumber leave me a long section of pipe (upside U) for future chemical injectors.



Does it matter if the acid is injected before or after the chlorine? If yes, why? If the acid needs to be injected before the chlorine, I can have it injected in the drain plug on the main pump. For the acid injection, I plan on fully automating it using a pH controller. I will have a pH probe inside a T for sampling the water. I will use a controller similar to Milwaukee MC122 to monitor the pH. When the pH is low, the controller will turn on the Stenner pump to pump in acid.

My real question is - where would you install the acid injector? Where would you install the pH probe?

Thanks Minh

 

[tim5055]

I think if you do a little searching on the site you will find that automation of pH is something that sounds better in theory than it is in practice. The sensors seem to be problematic.

But, acid injection before the SWG cell is probably the way to go. That is the approach the AutoPilot Total Control system recommends. This approach will help reduce scaling in the SWG cell. If you could move the SWG up to the "U" and inject the acid where the SWG is not it seems to me that it would work better.

 

[JoyfulNoise]

In the Pentair manual for their IntelliPH system, the installation instructions have the acid injection clamp shown as being 12" BEFORE the SWCG. There is some debate on these threads as to what is the best arrangement. The SWCG environment can be very alkaline due to the chlorine generation process and so, having acid injected before the cell can help reduce the pH inside it and help prevent scaling.

You absolutely SHOULD NOT inject any chemicals into your pump pot through the drain. Way too dangerous and you could potentially damage your pumps wet head with the extremely low pH.


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[mas985]

You absolutely SHOULD NOT inject any chemicals into your pump pot through the drain. Way too dangerous and you could potentially damage your pumps wet head with the extremely low pH.

I have done this before without any ill effect (see DIY acid dosing in sig). As long as you are careful not to inject too much acid, there is more than enough dilution that occurs within the pump basket so that the PH is not that much lower than when entering the pump basket.

 

[JoyfulNoise]

I have done this before without any ill effect (see DIY acid dosing in sig). As long as you are careful not to inject too much acid, there is more than enough dilution that occurs within the pump basket so that the PH is not that much lower than when entering the pump basket.

Ok. I guess my reasoning was from a safety perspective due to the possibility of leaks at the pump and/or connectors potentially loosening due to pump vibrations. Modifying the drain plug seems like a hassle. I should have been more specific. I would think if you had room anywhere else on the plumbing, the pump basket itself would be my last choice of places to inject acid.


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[mas985]

Actually, you don't need to modify the drain plug. There are several common barb fittings that can be used to screw directly into the drain plug opening and connect to the hose.

The advantage of using the drain plug is that it doesn't require any modification of the plumbing system and it really shouldn't matter if it is done there or further up the suction line as long as you are injecting the correct amount. Plus, I dilute the mixture 4:1 in the holding tank so it isn't as corrosive coming out of the tank as full strength.

However, some of us have moved the injection point to prevent injection while using the spa so the PH does not drop too much. That can be an issue if you have long sessions in the spa with the pump running.

 

[JoyfulNoise]

Actually, you don't need to modify the drain plug. There are several common barb fittings that can be used to screw directly into the drain plug opening and connect to the hose.

The advantage of using the drain plug is that it doesn't require any modification of the plumbing system and it really shouldn't matter if it is done there or further up the suction line as long as you are injecting the correct amount. Plus, I dilute the mixture 4:1 in the holding tank so it isn't as corrosive coming out of the tank as full strength.

However, some of us have moved the injection point to prevent injection while using the spa so the PH does not drop too much. That can be an issue if you have long sessions in the spa with the pump running.

Thanks for the explanation. I plan to check out your link as I'm planning on acid injection. I was thinking of just going with an IntelliPH but perhaps I'll consider the DIY route.


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[diverminh]

I think if you do a little searching on the site you will find that automation of pH is something that sounds better in theory than it is in practice. The sensors seem to be problematic.

What are the issues with the sensors? I been using pH probes for years in the aquarium hobby. Of course we don't have high flow over the probe head. Maybe that's what's causing the "problematic" sensor. I can always create a "vessel" that has a much slower flow thus reducing the chance of damaging the sensor. I realize the probe has to be replaced once every year or every other year.