The popularity of customizing aquarium setups by using none traditional materials and decorations is higher than ever right now.
Due to a number of different viral photographs on social media over the last couple of months, the number of people wanting to customize their tanks just keeps on increasing resulting in more and more questions about aquarium customization.
We have seen a number of people reaching out about using flagstone in an aquarium recently partly due to the customization that it offers you for your setup but partly due to how cheap flagstone can be due to some alternative options.
Unfortunately though, there are is a large amount of incorrect information online about using flagstone in an aquarium so we wanted to publish this article to try and help our readers better understand the material.
Our hope is that we will be able to help as many of our readers as possible better understand exactly what you should be doing with your flagstone to make sure that it is safe to use in your aquarium tank.
What Is Flagstone?
Flagstone is a type of sedimentary rock that is formed by the deposition of material over time.
This material is typically deposited in layers and then hardens into stone.
Flagstone is a very popular material for use in landscaping due to its durability, its wide range of colors, and its interesting texture.
Flagstone can be found in a number of different places around the world including the United States, Australia, Canada, China, and India.
Flagstone is typically composed of quartz, feldspar, or limestone though it can also be found with a number of other minerals as well meaning that flagstone from different locations can have a totally different mineral makeup!
There are some more modern rocks that are marketed as “flagstone” that are made from synthetic materials often being safer for use in aquariums but these are not traditionally flagstone.
Is Flagstone Safe To Use In An Aquarium?
Due to flagstone being a sedimentary rock that is made up of deposits of a large number of different minerals over an extended period of time, different flagstone slabs from the same location can have a very different mineral makeup.
This means that some of the slabs can be perfectly safe for your aquarium where as others may cause serious issues with your tanks water parameters.
If you have ever seen the heated discussions on social media about using flagstone in an aquarium, this is usually the reason that people on both sides of the argument think that they are right.
Flagstone is a generic term and does not describe a mineral composition for the rock meaning that some flagstone is aquarium safe where as other slabs of flagstone is not aquarium safe.
Now, synthetic flagstone is usually made from a smaller number of minerals with this usually being easier and safer to use in an aquarium but even in this situation, depending on what the synthetic flagstone is made from, it may not be safe for use in your aquarium.
How Can I Check If My Flagstone Is Aquarium Safe?
A very common yet highly inefficient method of checking if flagstone is safe for use in an aquarium is to drop some white vinegar on the flagstone to see if they react with each other.
The traditional thinking is that if the white vinegar does react with the minerals in your flagstone by fizzing and producing gas then it’s not safe for use in your aquarium.
Although this is correct in the sense that any flagstone that reacts with white vinegar is often not safe for your aquarium, it does not mean that all flagstone that does not react with your white vinegar is aquarium safe either.
There will always be a risk when using natural or synthetic flagstone in your aquarium.
In our opinion, the best way to check if your flagstone is safe for use in your aquarium is to submerge it in a container filled with water and leave it for a week.
Then you test the water in this container with your water test kit to see if there are any issues with your water parameters, ideally, an advanced water test kit that tests for as many parameters as possible.
This will give you a better idea of any potential issues that the flagstone may cause in your aquarium and then you can make a more informed decision on if you want to add the flagstone to your aquarium.
Why Do People Use Flagstone In An Aquarium?
Most people use flagstone in their aquarium due to its low price and how customizable it is.
You can use flagstone as a base for your aquarium or break it down into smaller parts to use as decorations or to make caves.
There really are a wide number of use cases for flagstone in an aquarium provided the flagstone is safe for use in your tank.
If you have the time available and like to customize your tank then there really are some great aquarium setups that you are able to generate that use flagstone as their main material.
Can Flagstone Replace Substrate?
Flagstone does not replace substrate in planted tanks as it offers minimal nutrients for your plants.
A common mistake that we see people make time and time again is to think that flagstone can work with all aquatic plants due to some of the flagstones planted tank setups seen on social media.
Some aquatic plants don’t require their root structure to be in substrate allowing you to use these plants in a flagstone setup with ease.
This will come down to a plant by plant basis though so you will have to research the specific plants that you are considering using in your aquarium to see how they need their roots anchoring.
If you want any plants in your tank that need their roots in substrate then you will have to work out a way to add a suitable substate to your tank.
This can be as simple as you having part of your aquarium base as substrate and part as flagstone or you may want to add pots with substrate in them that sit on your substrate for your plants to grow from.
How Do You Get Flagstone Ready For Use In An Aquarium?
We would always recommend that you use the method covered earlier in the article to try and test if your flagstone is safe for use in your aquarium where you submerge it in a container of water for a week before you do anything else.
While submerged, most potentially harmful things will end up washing off your flagstone anyway making it much easier to prep your flagstone for use in your aquarium.
Most people just wash their flagstone down after deciding that it is safe for use in an aquarium though and in many setups, this can be totally fine and safe to do.
If you are wanting to cut your flagstone slabs down to a smaller size for your design then remember to rewash it after cutting it to remove any dust build up from the cutting.
Ideally, you will cut your flagstone down to size prior to submerging it to test if it changes the water parameters in your test container though.
This is due to the same flagstone being able to have different layers of minerals from its outside to its core.
Just because its initial outside layer of minerals may not change your water parameters does not mean that its inner layers that may be different minerals will not cause issues.
Is Flagstone Reef Safe?
We would never recommend that you use flagstone in a reef tank as its just not worth the risk in our opinion.
Even a basic reef tank setup is usually worth more than a freshwater or even a generic saltwater setup due to the corals and anemones in the tank.
In many cases, the corals and anemones in a reef tank are far more sensitive to changes in their water parameters than their freshwater counterparts.
We know that there are some people on social media who have used flagstones in a reef tank and have managed to build out a beautiful setup but for the average person, we would never recommend it.