This is not a duplicate... pls read the whole question....

I am attempting electrolysis of brine (tap water + table salt). I am using HB pencil lead (graphite) as my two electrodes. I am using 12 volt- 1.5 amp DC power supply (using an adapter from the wall). The solution is getting slightly alkaline (~8 pH) and hydrogen is confirmed by pop sound.

However, the whole solution is getting filled with some brown particles (resembling Dirt). If by chance my alligator clips get submerged, the get a brown coating (which I am able to wash it off).

What are this brown particles?

I have a few theories: 1. Pencil lead also contains clay.
2. Something with the water (though it is filtered)

I had attempted this earlier (~3y) and had a similar but a more dramatic result. Then I used iron/steel electrodes and they became completely brown. The plastic container I used also became completely brown coated. I was unable to wash it off.

  • $\begingroup$ Is the tap water coming straight from the ground? (groundwater) $\endgroup$ Nov 14, 2016 at 11:03
  • $\begingroup$ @HugoWoesthuis, IDK, Ill try to check where my water is coming from. Your answer seems the likliest but any idea how to fix it!?! $\endgroup$
    – darkspine
    Nov 15, 2016 at 11:55
  • $\begingroup$ @Zhe, I am getting bubble at both sides... $\endgroup$
    – darkspine
    Nov 15, 2016 at 11:55
  • $\begingroup$ You're using a significant over voltage, so you might be oxidizing both to oxygen gas and to chlorine gas. Is the proportion of oxygen to hydrogen as expected or less? $\endgroup$
    – Zhe
    Nov 15, 2016 at 14:44
  • $\begingroup$ Concerning your first theory: Typical HB pencils contain a mixture of about 2 parts of graphite and 1 part of clay. $\endgroup$
    – user7951
    Nov 17, 2016 at 13:40

1 Answer 1


If your tap water is groundwater, it will contain a lot of metals that will start rusting if reacting with O2 and Cl (your salt). The reaction causes the brown particles (rust/ Ferric Oxide). The only way to prevent this is to filter the water continuously. This reaction is also common with salt-electrolyzed pools. Here is a forum thread that has exactly the same issue you have.

This was the answer:

That looks like rust, Ferric Oxide, exactly! However, the cell should be Titanium, it contains no iron, but that doesn't mean it can't oxidize. Or "Rust", all metals do, Ti's oxidation would be white and powdery.

So either there is a non Ti component inside that cell that contains iron, such as steel that is breaking down, or there's something upstream of it, a Ferrous metal that's rusting, thus producing Ferric Oxide and dribbling down the pipe and into the cell. Is there any on the upstream side of the cell? If not, then it has to be localized to inside the cell.

Another though is that you have a very high iron content in your water, mixed with the electrolysis process is causing it to oxidize on the anode, where it combines /w oxygen molecules in the water to form rust, Fe2O3. This would keep it localized to the cell, and not be upstream, only at the cell, since that's the catalyst, or source and slightly downstream as the flow of generated Ferric Oxide tapers off. This shouldn't effect the Ti plates though, just simply clean them with MA and you're golden!! Ti is virtually indestructible, so they should be fine.

EDIT: Hayward says to submerge it just to the top of the cell, so the wiring harness, the electronics on the cell are not touching the acid, coiling the harness may be helpful prior to immersing. 4:1 dilute, 1 gallon of water to 1 quart of MA. And remember, always, always add the acid to the water, never, ever the other way around. The manuf. says to soak for a few, then rinse with a high pressure hose, then repeat if needed, until the plates are clean. BTW, Acid attacks Oxides, including Ferric Oxide.

Full thread here

Related Stackposts: Salt product in water electrolysis

  • 1
    $\begingroup$ I was under the impression "rusting" is used to refer to the corrosion of Iron or iron-based alloys O.o. Personally, I doubt whether that's rust. I don't really see what the chlorine would do to promote rusting (if it is rust), perhaps the H+ would do the job? $\endgroup$ Nov 14, 2016 at 13:16
  • $\begingroup$ @AaronAbraham It could be, but considering groundwater with so many metals that can react with each other, it will be unlikely to be completely sure if the brown particles are rust. I searched on Google and found out that this is a common thing in pools with salt-electrolyse. They say that if you don't filter the water correctly, and the salt (NaCl) is added too early, the metals in the water will react with the O2 and the salt together (I doubt salt plays a role in this, but the oxygen is for sure), making the water brown (rust). $\endgroup$ Nov 14, 2016 at 19:39
  • $\begingroup$ Any idea how to fix this without continuously filtering., I only have one water source... All help appreciated.. $\endgroup$
    – darkspine
    Nov 15, 2016 at 11:54
  • $\begingroup$ @Srathi00, you can't. Use normal water/groundwater and filter or consider using demi-water (demineralized water). $\endgroup$ Nov 15, 2016 at 14:56

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