Citric Acid

[griss]

I’ve never used citric acid before. I got some old dry (Fiji, Tonga, etc) rock that originally was 1990s wild collected live rock from a friend. I’m wanting to give it an acid bath to reduce potential phosphates.

I don’t want to deal with Muriatic acid and several on here have suggested citric acid. With the cold weather we’re having I don’t think I can do this outside so, can this be done inside? I ask because I see people use it to clean skimmers, kitchen and bathrooms, etc. So, I assume, it would be safe give the rock and acid bath inside????

 

[Uncle99]

I’ve used it for years to clean my wavemakers and gear.
Not as harsh as vinegar, but of course, more expensive.
Works well for me. No issues. Always used inside.

 

[griss]

I’ve used it for years to clean my wavemakers and gear.
Not as harsh as vinegar, but of course, more expensive.
Works well for me. No issues. Always used inside.

Thank you.

 

[wvned]

The problem is this. Muriatic (HCl) acid is a strong acid. Acetic and citric acids are weak ones.
This is based on their chemical properties.
Strong acids completely dissociate in water, producing a high concentration of hydrogen ions, while weak acids only partially dissociate, resulting in a lower concentration of hydrogen ions.
Strong acids will work much more quickly and break down more chemically stable carbonates that weak acids may not work on or may take a month to dissolve.
Yes it takes a bit of care to use and can ruin a shirt in 2 seconds but it I safe enough to be sold by the gallon at Home Depot.

 

[Jimbob]

It seems for your stated purpose, the citric acid should work just fine, and might even be preferred given that is is a weaker acid in comparison to HCI?

As wvned mentions, the stronger the acid, the more quickly it breaks down carbonates... this is ideal when wanting to remove carbonate deposits from equipment. Given you are working with rock and that you only want to "wash" potential phosphates out of your old dry rock rather than dissolve the rock entirely, the weaker acid might be easier to manage?

 

[wvned]

I have read about using acid to open the pores in rock, is that why you want to use it? I thought phosphates freely dissolved into water.

 

[griss]

I have read about using acid to open the pores in rock, is that why you want to use it? I thought phosphates freely dissolved into water.

Dual purpose. Open the pores on the rock.

Over time, from everything I’ve heard over the years (including from Randy Holmes-Farley), the rock can absorb phosphate. Then, when the phosphate concentration drops in the water column, it can leach out and cause algal blooms. To counter that, many recommend the acid bath to dissolve the outer layer or rock and remove the phosphates.

I believe the rock my friend brought me was in his LFS and later transferred between multiple tanks. I know he never used things like copper but, with rock this old, I’m operating under the assumption that it probably has absorbed phosphate.

 

[wvned]

I am thinking the rock you have is no different than having rock in a running tank and removing the phosphates.
If you do a water change or dose LaCl and do testing the P quickly goes back up like you accomplished nothing. But over many repetitions or daily dosing of LaCl the running value does come down. I have seen my rock source P back into the tank. It becomes less and less over time.
This makes me think the phosphates are not held in any way by the rock. If the concentration in the surrounding water is lower they come out.
This is like getting soap out of a sponge you cant squeeze and ring out. You keep changing the water because it is the concentration difference that speeds up the process.
Acid may do something to the pores of the rock so that might be of some value removing old coralline but I think I would go easy on that or some might become crumbly. The rock we used to get wasn't always the hard mined stuff we get now.

 

[griss]

I am thinking the rock you have is no different than having rock in a running tank and removing the phosphates.
If you do a water change or dose LaCl and do testing the P quickly goes back up like you accomplished nothing. But over many repetitions or daily dosing of LaCl the running value does come down. I have seen my rock source P back into the tank. It becomes less and less over time.
This makes me think the phosphates are not held in any way by the rock. If the concentration in the surrounding water is lower they come out.
This is like getting soap out of a sponge you cant squeeze and ring out. You keep changing the water because it is the concentration difference that speeds up the process.
Acid may do something to the pores of the rock so that might be of some value removing old coralline but I think I would go easy on that or some might become crumbly. The rock we used to get wasn't always the hard mined stuff we get now.

Point taken. If I do this, it will be a quick acid bath using a weaker solution (another reason I’m using citric instead of Muriatic).

Where do you source your LaCl? In all the years I’ve been in this hobby, I’ve never used it.

 

[wvned]

I get Phosban-L by the gallon from Premium Aquatics. To use it you dilute it to 33%. 1000ml phosban and 2000 RODI.
No Lanthanum registered on my last ICP. I assume it would read.

 

[griss]

I get Phosban-L by the gallon from Premium Aquatics. To use it you dilute it to 33%. 1000ml phosban and 2000 RODI.
No Lanthanum registered on my last ICP. I assume it would read.

Thank you my brother