Water chemistry question regarding pH, redox, soda ash

[diggity]

So a couple weeks ago I installed a soda ash injection system to prepare our water for iron removal. I extolled the virtues of injecting soda ash, as it seemed to improve overall water quality more than expected. I had not yet installed our new Katalox Light filter for the iron.

Well now the Katalox Light system has been installed, so our system now looks like this:

Well ---> soda ash injection ---> contact tank ---> Katalox Light ---> softener

I'm not quite sure yet how good a job the KL is doing at removing the iron, as my iron test kit is on back-order for a few more days. But in the meantime, out of curiosity, I tested the pH at the kitchen sink and found that it has gone down! So now our pH starts at 5.25, gets raised by soda ash to about 7, then drops down to about 6 after it goes through the KL.

I'm just wondering what's going on here, and if it's a problem. It has been a LONG time since I've had any water chemistry classes! ;-)

Is the carbonate being converted to carbon dioxide? We have noticed a tiny bit of cloudiness which clears up almost immediately when you fill a glass of water. I had assumed it was air still working its way out of the system, but maybe it is carbon dioxide bubbles? In other words, carbonic acid? And if this is the case, am I wasting some of the KL's oxidative power on producing CO2? Or am I totally off-base? Or over-thinking it?

I'm just a little disappointed because for a few glorious days, we finally had pH 7 water at the sink and now it's back down again. :-(

Thanks in advance!

 

[Reach4]

Clearly you have been doing your study. I would certainly hope the reaction of Na2CO3 has enough oxygen and would not consume dissolved O2.

How often do you backwash the KL, and is the sink pH affected by that?

I would crank up the soda ash injection to bring the water out of the contact tank to maybe 7.5. That is not not based on any experience.

 

[Sponsor]

 

[diggity]

Thanks for the reply Reach4. I'll take your advice and try cranking up the feed rate on the soda ash. Fortunately pH is pretty easy to monitor, so I can keep an eye on it pretty well. Right now the KL system is backwashing every 3 days - this was a bit of a stab in the dark and I have no idea if that is too frequently or not frequently enough. When I finally get my iron test kit I'll be able to keep a close an eye on that too.

I'm manically obsessed enough at the moment to try injecting sodium hydroxide (lye) instead of sodium carbonate, but I can't seem to find it locally...