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How can I clean terracotta decorations?


KyleKVK
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2 hours ago, KyleKVK said:

I have an apisto cave covered in algae and I don’t know how to get rid of it. Can I dip it in peroxide or vinegar?

It’s harmless but it’s an eyesore

Remember that unglazed terracotta is porous clay. So, whatever solution you use will be absorbed by the terracotta. Also, even though you can kill the algae pretty easily, the terracotta may retain stains, similar to having a coffee stain on your shirt. 

Because of this property, I would avoid using anything that could later leach out into your aquarium. So, I think vinegar and chorine bleach are a thumbs down. 👎 E.g., vinegar is an acetic acid solution. Acetic acid is pretty stable and does not evaporate. So if you use vinegar, the terracotta will absorb the acetic acid, which could later be released into your aquarium and drop the pH. 😳

I think I would try hydrogen peroxide (H2O2) first. In my experience, it works pretty well at killing algae. It is also mild bleach, so it might help get rid of the stains.  The benefit of peroxide is it does not leave any chemicals in the terracotta. Whatever soaks into the terracotta quickly breaks down into oxygen (02) ⚛️ and water (H2O). 🌊 Soak the terracotta cave in a bowl/bucket containing 3% hydrogen peroxide overnight. 3% is typically what you get from the drugstore. Do not use a higher percentage! Let the terracotta dry.

At this point, the algae is dead. However, if it still looks "dirty," you could try boiling it in water and/or hand-scrubbing it, as @H.K.Luterman. You can also try these in the reverse order—boiling in water then soaking in H2O2—but I suggested soaking first because that method is the least amount of work! And I am lazy, haha! 😉

Let us know what works for you! 🤓
 

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Starting with a peroxide soak and a toothbrush/scratchpad is probably the safest and easiest way to go.   As the others have implied, the peroxide will naturally break down and be gone in hours.  Having bleached aquarium decorations in the past, I found that it may take days of soaking and sun to get all of the bleach out of the terracotta

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Something a bit offbeat you might want try is denture cleaner. You'll still want to rinse the cave thoroughly afterward as the active ingredient in it is often a bleach or citric acid, but it's safe enough for people to use on a daily basis so it shouldn't be overly hazardous for fish. I would rinse the cave and soak it thoroughly after use, but those denture cleaning tablets have a lot of uses other than cleaning dentures. 

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14 hours ago, Anita said:

Soak the terracotta cave in a bowl/bucket containing 3% hydrogen peroxide overnight. 3% is typically what you get from the drugstore. Do not use a higher percentage! 

@Anita should you use the 3% hydrogen peroxide straight out of the bottle or dilute it in water?  And should you rinse it off with clear water before you let it dry and put back on the tank?

Edited by seakitty
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I wouldn't be too worried at any concentration*. 12% seems to be most economical to buy. It's reactive, it will react, then it's gone, unlike "poisons" that may linger or break down / react into nasty compounds (chlorine). That being said, no point using higher concentration than needed! I recall a certain discomfort (and discoloration) in fingertips and nails after ignoring the common sense caution of gloves, but that was 30 or 40% H2O2. I haven't used it in relation to aquaristics myself.

Edit: 3% is the safer and therefore probably more practical concentration. Be responsible.

Edited by darkG
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12 hours ago, seakitty said:

@Anita should you use the 3% hydrogen peroxide straight out of the bottle or dilute it in water?  And should you rinse it off with clear water before you let it dry and put back on the tank?

Sorry for the late response, it's been a hectic weekend. You can use 3% peroxide straight out of the bottle. I suggest letting it dry because the drying process also helps kill the algae. No need to rinse it off because as @darkG noted, no "nasty compounds" get left behind. A small amount (measured in milliliters) of H2O2 can be poured into an aquarium to kill algae. I have done this and also have used a very dilute (much, much lower than 3%) solution of H2O2 solution as a dip to remove algae on plants. 

11 hours ago, darkG said:

I wouldn't be too worried at any concentration*. 12% seems to be most economical to buy. It's reactive, it will react, then it's gone, unlike "poisons" that may linger or break down / react into nasty compounds (chlorine). That being said, no point using higher concentration than needed! I recall a certain discomfort (and discoloration) in fingertips and nails after ignoring the common sense caution of gloves, but that was 30 or 40% H2O2. I haven't used it in relation to aquaristics myself.

Hmm, yeah, I'm not too sure about this. I guess, personally, I would not recommend using 6% or 12% peroxide. At these concentrations, the peroxide is a pretty strong oxidizer and definitely could burn wet skin. For example, hair bleaching products contain 6%-10% peroxide. And you will notice that stylists always wear gloves when highlighting or bleaching someone's hair. Higher concentrations of peroxide could also bleach your carpet, upholstery, or clothing if you spill any. Not to be an alarmist, but here is the material safety data sheet (MSDS) for 6% hydrogen peroxide

Nor do I think you can save money buying 6% and 12% peroxide. For example, I believe you will discover that one 16 oz bottle of 6% costs roughly $15, compared to two 16 oz bottles of 3% (roughly $2-$3 apiece). As soon as you crack the seal on the bottle, the peroxide reacts with the atmosphere and begins to degrade. The higher the percentage, the faster the rate of degradation. It would a shame to spend the extra money on 6% peroxide that six months later is considerably weaker than what you paid for.

At any rate, we do seem to agree that you don't need anything stronger than 3%. The peroxide breaks down during the soak, so you cannot reuse it. Just pour it down the sink. Good luck! Please let us know how it works for you! Photos would be awesome. 😎

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I am not sure you need hydrogen peroxide at all 🙂 but yeah, if 3% is sufficient, it is probably more practical. I haven't bought any for years, I seem to be able to source 32 oz 12% for $12, if my conversions check out, but this may of course vary across countries.

My main point is that hydrogen peroxide may be hazardous (I did mention that I hurt myself), but it is not toxic. Often, the way things (chemicals in particular) are problematic is ignored, so that perfectly usable materials are not used while truly noxious compounds are happily dispersed (flushing down lead, antibiotics, nitrite test fluids...).

Anyway, your point is well taken. I should be more cautious and consider the whole picture ("but guy on the internet said it was safe!").

Cheers!  

Edited by darkG
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5 hours ago, darkG said:

I haven't bought any for years, I seem to be able to source 32 oz 12% for $12, if my conversions check out, but this may of course vary across countries.

You are a magic shopper! Don't lose that source. 😎

5 hours ago, darkG said:

My main point is that hydrogen peroxide may be hazardous (I did mention that I hurt myself), but it is not toxic. Often, the way things (chemicals in particular) are problematic is ignored, so that perfectly usable materials are not used while truly noxious compounds are happily dispersed (flushing down lead, antibiotics, nitrite test fluids...).

Anyway, your point is well taken. I should be more cautious and consider the whole picture ("but guy on the internet said it was safe!").

Cheers!  

You did indeed! My friends would reveal to all that I am OCD about researching, well... pretty much everything. They will also tell you I am overly cautious about chemicals and what not. I certainly agree that we need to be more conscientious with our chemical disposal. Between you and me, poor @KyleKVK's head is probably spinning. Warm regards @darkG 🥰

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