Complete guide to treating synthetic rocks and regenerating natural rocks for marine reef aquariums.
Rocks and colonizable substrates in general have always been one of the main drivers of our systems.
In the past, live rock was readily available from stores, wholesalers, and importers. But, from an ecological point of view, fortunately, increasingly strict regulations have reduced imports to the point where live rock is now almost impossible to find.
Today, with a view to reducing human impacts, inert materials are preferred, such as "synthetic" rocks, natural fossil-origin or dead rocks from decommissioned aquariums.
Treating rocks before adding them to an aquarium is essential to prevent the release of organic material residues or unwanted chemicals and to stabilize water chemistry during a critical phase such as setting up a new aquarium.
Untreated inert rocks can release nutrients, metals, production residues, and various other contaminants into the system, which can considerably prolong and complicate the initial colonization phase of the aquarium.
A few years ago, we launched the first trials of a treatment specifically for inert synthetic and natural rocks.
After analyzing the data collected during the prototyping stages, we realized that the process we were using was too complex and labor-intensive for hobbyists to use effectively, and would only be suitable for industry professionals equipped for this type of work.
We therefore chose to simplify the process, reduce the number of treatments, and use materials that are less hazardous, less expensive, and easier for hobbyists to find.
Once we had achieved results comparable to professional treatments, we decided to make the project "open source".
The reduction of wild harvesting, the use of low-impact materials, and the possibility of regenerating and recycling natural rocks from decommissioned aquariums ultimately convinced us that the best way forward was to make it freely available to everyone.
This short article offers a simplified two-stage protocol for preparing synthetic rock using an acidic citric acid solution and an oxidizing/basic bath with sodium percarbonate.
Why treat synthetic rock?
Synthetic, regenerated, or quarry-mined natural rocks represent an ecological and sustainable alternative to live rock collected from nature.
However, it is very common for these to carry heavy metals, chemical residues, contaminants and/or excess nutrients that could significantly affect water parameters and system balance, making cycling extremely long and laborious.
L'the idea is to bring the material to extreme conditions that it will no longer encounter once the rocks are placed in the system.
L'use of acids, oxidizers, and bases ensures effective removal of the vast majority of contaminants typically present.
The Three-Stage Treatment Protocol
Stage 1: Citric acid treatment
Acid washing is essential for removing residues of alkaline materials and surface calcium deposits from synthetic rock.
In dead rock, it helps open the pores and channels present, physically removing the surface layer, which is generally more contaminated.
L’citric acid, a weak organic acid, is safe and readily available, as well as effective at removing calcareous encrustations and clearing channels blocked by residue from coralline algae and other encrusting organisms.
Solution preparation:
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Dilute citric acid in RO or demineralized water to obtain a 2.5-5% solution.
This concentration effectively cleans the first surface layers without excessively damaging the rock structure.
For a 2.5-5% solution, dissolve 250-500 grams of citric acid in 10 liters of water. -
Fully immerse the rocks in the citric acid solution and leave them to soak for 12-24 hours, stirring the solution from time to time.
For natural rocks, check that the first surface layer is actually removed.
A few millimeters are generally enough, but if the material is particularly contaminated, you can use a more concentrated solution, leave it to soak for longer, or repeat the bath.
Cloudy water and partial dissolution of the calcareous material are completely normal and are the intended result.
Check the process regularly to prevent excessive material dissolution.
With ceramic synthetic rocks, however, you will not see surface dissolution, and the water will become much less cloudy.
Don't worry: this is normal. In that case, what matters most is making all the contaminants inside them and any production-related impurities that are sensitive to acid baths react.
Intermediate Rinse:
After the acid treatment, rinse thoroughly to remove any residues.
This step is crucial to prevent acidic residues from affecting the oxidizing bath.
You can use a pressure washer or simply scrub with a stiff-bristled brush under running water.
Be thorough and clean the surface as carefully as possible.
At this intermediate stage, you can use tap water, as long as it is not excessively contaminated.
If you have any doubts about the quality of your tap water, play it safe and use osmosis or demineralized water.
For better results, or if the rocks are particularly dirty, you can soak them again for another 12-24 hours in osmosis water, taking care to change the water a couple of times.
Phase 2: Sodium percarbonate treatment
Sodium percarbonate is an extremely versatile compound that serves a dual purpose in treating synthetic rocks: it acts as an oxidizer, removing any residual organic substances, and as a basic buffer to restore a neutral or slightly alkaline pH.
When dissolved in water, sodium percarbonate releases hydrogen peroxide and sodium carbonate, providing deep cleaning and neutralizing the pH.
Solution preparation:
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Dilute the sodium percarbonate in osmosis or demineralized water to obtain a 2.5-5% solution.
This concentration enables effective neutralization of any remaining acidic residues, oxidation of organic residues (nutrient sources), and contaminants sensitive to oxidizers.
For a 2.5-5% solution, dissolve 250-500 grams of sodium percarbonate in 10 liters of water. -
The water temperature (around 30-35°C) can speed up the reaction and improve the effectiveness of the solution.
Treatment procedure:
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Immerse the rocks treated with the acid solution in the sodium percarbonate solution and leave them to soak for 12-24 hours.
This step allows the sodium percarbonate to oxidize any organic residue while also stabilizing the pH. -
Stir the solution occasionally to optimize contact between the rocks and the solution.
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L'Any foam produced is completely normal and is due to the presence of organic residue or residue from the acid bath.
Final rinse:
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After the sodium percarbonate bath, a thorough rinse is essential to remove any treatment residue and remaining contaminants.
This step ensures that the rocks are ready and safe to add to the aquarium. -
Rinse the rocks thoroughly, this time strictly in reverse osmosis water, using a stiff-bristled brush.
If the rocks are particularly dirty or contaminated, they can be soaked again for another 12-24 hours in reverse osmosis water, taking care to change the water a couple of times.
Phase 3: EDTA treatment
L’EDTA (ethylenediaminetetraacetic acid) is a powerful chelating agent used to bind and remove any heavy metals that may be present inside synthetic rocks. This step is essential for reducing the risk of toxic elements, such as copper, lead, or zinc, gradually leaching into the aquarium and compromising the health of marine organisms.
Solution preparation:
- Dissolve 10 g of EDTA in 1 liter of reverse osmosis or demineralized water.
- To ensure a stable, optimal pH (8–9), add 1 teaspoon of baking soda per liter of solution.
- If you have a pH meter, check the readings periodically: if the pH drops below 8, add a little more bicarbonate in small amounts until it returns to the correct range.
Treatment procedure:
- Immerse the previously rinsed rocks in the EDTA solution and leave them to soak for 48–72 hours.
- To increase the effectiveness of the treatment, keep the solution moving gently using a pump or, alternatively, a simple air pump. This promotes surface exchange and improves metal chelation.
Final rinse:
At the end of the treatment, rinse the rocks thoroughly in plenty of reverse osmosis water, preferably changing it a couple of times.
This step is essential for removing every trace of EDTA and the metal complexes formed, making the rocks completely safe to add to the aquarium.
Drying phase:
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Leave the rocks to air-dry in a clean, dry environment.
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After drying, the rocks will finally be ready to add to the aquarium.
Additional considerations and precautions:
- Always wear gloves and safety glasses.
- Work in a well-ventilated area.
- Avoid using products not described in the protocol.
Although we have selected relatively safe materials, working with acid and oxidizing solutions always requires care.
We recommend wearing gloves and safety glasses to avoid accidental contact with the chemical solutions, and carrying out the treatments away from children and animals.
Although sodium percarbonate and citric acid are relatively safe, they can release gases or odors, so we recommend always working in a well-ventilated area.
To avoid unnecessary risks or the production of toxic or harmful gases, do not use bleach or any other ingredients not described in the protocol.
Advantages of the two-component treatment protocol:
The two-step treatment with citric acid and sodium percarbonate offers a comprehensive, economical, and reliable approach that ensures the biological material remains stable, effectively removes the most common unwanted substances inside the rocks, and completely eliminates any manufacturing residue.
The treated rocks are now ready for long-term use, helping to stabilize the system without altering the water parameters or delicate biological balance.