Things to Check Before Putting Fossils in a Fish Tank

Guest Post By Maria Foster: A poet, a writer, and a full-time RVer. Loves fishing with her four-legged friend.

Maintaining a fish tank can be fun and exciting. You can add wood, plants, rocks, and stones to it — even fossils. The possibilities are endless!

Before you dash to the nearest beach to hunt for fossils, take a breath. There are important things to consider before decorating your fish tank with them. Your fish tank is a self-contained ecosystem on its own that is host to a variety of organisms and microorganisms such as algae, bacteria, and tardigrades. It’s therefore important to consider how anything you add to it might affect the delicate balance inside your aquarium. In this article, we’ll guide you through everything you need to know and do before adding fossils to your fish tank.

How Are Fossils Created?

Fossils are the preserved remains of plants and animals. When the conditions are just right and an organism doesn’t decay or get eaten, its physical shape and form are left behind in sediment. The oldest fossil discovered is estimated to be 3.5 billion years old. These organisms become fossils by:

  • Authigenic preservation. Molds or casts of destroyed or dissolved organisms.
  • Carbonization/coalification. Carbon remains in the specimen where other elements are removed.
  • Permineralization/petrification. Rock-like minerals slowly slip into the original organic tissues replacing them with calcite, pyrite, and silica thereby forming a rock-like fossil, which can be both hard and soft.
  • Recrystallization. The hard parts of an organism revert to more stable minerals. Alternatively, small crystals turn into larger ones.
  • Replacement. The hard parts of an organism are replaced by minerals like calcite, iron, pyrite, and silica.
  • Unaltered preservation. Parts of plants and insects are trapped in the sap of a tree.

Are Fossils Safe for Fish Tanks?

Fossils can have mineral or metal content such as calcium which can potentially harm your fish. There are tests that you can do at home to determine if a fossil is safe for your aquarium. An even better option is to have a geologist analyze the content of your fossil.

How can a fossil affect your fish tank? The carbonate content in fossils can negatively drastically affect your aquarium’s pH level and the alkalinity of the water so you should never add a fossil without inspecting it first. Likewise, aquarium water can completely dissolve some rocks and fossils, destroying your valuable specimen.

Rocks To Avoid

You might have noticed a wealth of fossils sold online and in pet shops. However, just because they’re being sold for aquariums doesn’t mean they’re right for the one you have. In general, you should steer clear of pointed and sharp-edged rocks since they can injure your fish.
Additionally, saltwater and freshwater aquariums will have different rocks in them. What’s safe for one may not be good for another because aquarium rocks can affect the water hardness and pH levels of your fish tank. You should also consider the individual needs of the species living inside it. If you have a saltwater tank, the following rocks and decorations should work fine:

  • Crushed coral
  • Dolomite
  • Geodes
  • Limestone
  • Marble
  • Shells

If you have a freshwater aquarium, consider the following rocks:

  • Lava rocks
  • Quartzite
  • Rainbow rocks
  • Petrified wood
  • Onyx
  • Texas holey rocks
  • Sandstone
  • Granite

Even if a rock is listed safe for your type of aquarium, there’s no telling if it might hold minerals or fragments that are unsafe for your fish tank. Therefore, it’s always best to run any rock or fossil you want to add through a test before adding it.

How to Determine the Safety Quotient of a Fossil

Step 1
Test the hardness of the rock with a steel knife. If the fossil is harder than the steel, it’s safe but if it’s soft and you’re able to make etches on it or small pieces come off, proceed with the rest of the steps to determine if it’s safe to add.

Step 2
To check the safety quotient of a rock that didn’t pass the strength test outlined in the first step, check for carbonated materials within the rock by checking its pH level. Here’s how:

Method 1
Since vinegar erodes calcium carbonate, you can use vinegar to detect carbonates’ presence in fossils. Pour a small amount of warm vinegar on the fossil. Hold it close to your ear. If it fizzes, it has carbonates in it.
However, vinegar is a weak acid so it won’t always produce that audible fizz. With a magnifying glass, look for fizzing and bubbles on the surface where you placed the vinegar.

Method 2
Based on the same principle, you can also use muriatic acid for testing. Though we outline the instructions here, it shouldn’t be the first course of action especially for minors and individuals with limited experience handling industrial chemicals.
Vinegar works just as well without the risk of blindness, skin burns, and harming your respiratory system. If you must use this method, always use the prescribed safety gear and exercise utmost caution.

Method 3
You can also test the fossil by immersing it in a clear glass container filled with tap water for a couple of weeks. Check the pH level of the water before and after. If you don’t have access to a pH meter, observe the fossil for signs of dissolution or decomposition.
A small change in the pH levels shouldn’t concern you but if the pH level drastically changes, avoid putting it in the fish tank as it can endanger your fish’s health causing shock and even death.
If your fossil has mineral streaks such as red or green rust, don’t bother to test it, it’s not a good candidate.

A green beautiful planted tropical freshwater aquarium with goldfish

Are Carbonates Good for Your Fish Tank?

Water hardness refers to the amount of dissolved minerals in water and is a vital parameter when you have a freshwater aquarium. One of the things you need to keep an eye on is the carbonate level in your fish tank. Your aquarium’s carbonate level is important because it contributes to general water hardness and can be used to boost alkalinity (the water’s ability to resist changes in pH levels). How? Carbonate binds to acids when they appear which has a neutralizing effect.

In the right amounts, calcium carbonate is useful for fish to build stronger bones, regulate metabolism and their ion exchange. You therefore need to maintain certain carbonate levels to ensure the health, growth, and longevity of your fish. When the carbonate hardness dips too low, it can cause your fish tank’s pH levels to fluctuate drastically which can harm and even kill your fish.

While water hardness ranges from soft (0 to 50 ppm) to very hard (200 to 400 ppm), a hardness of 60 ppm and above is generally good for fish. Pay close attention to the carbonate hardness levels that the life in your aquarium needs to thrive.

How pH levels work

Your aquarium’s pH levels determine the acidity or basicity of the water. It uses a logarithmic scale that considers a pH level of seven neutral. Anything below seven is categorized as acidic while water above seven is classified as basic or alkaline.

Why is this an important consideration for your fish tank? The pH level in your aquarium is important because sudden changes to it (even if minimal) can stress your fish and affect their well-being.

To make pH levels work for you, identify the pH range that is acceptable for the type of aquatic life you’re taking care of and make sure that the pH level doesn’t change by more than 0.3 units per day. Any more will cause stress to your fish.

Most freshwater tropical fish will thrive between 6.8 and 7.6 pH. Keep in mind that your aquarium’s pH levels will decrease over time as a result of the breakdown of organic material. One of the best ways to deal with this is by replacing some of the water periodically.

When the amount of carbonate goes up, your water’s pH level rises too. If you have saltwater fish in your tank, this shouldn’t be a problem. However, the water hardness required by guppies, malees, and goldfish will be different from what marine fish or African cichlids need so make sure to always take the kind of fish you have into account.

If the tank is big and the fossil is significantly smaller, it should pose a lower health risk to your fish no matter what minerals it contains. You only need to regularly change the water in the tank to make it more habitable. There are certain chemicals, however, that are deadly to certain fish and many invertebrates. Copper is one such example. When placed in a fish tank in even small amounts, it can wipe out all the life in your aquarium that isn’t a fish. You need to be careful because copper is found in many materials such as azurite, malachite, and turquoise.

Calcium Carbonate and Your Fish Tank

One thing you need to always check for is the possible presence of calcium carbonate (CaCO3). On their own, calcium, carbon, and oxygen in small to moderate quantities aren’t likely to do any harm to the life in your fish tank. However, the chemical compound calcium carbonate dissolves quickly in freshwater and could potentially leave behind residue that can clog your filters. This is why rocks with high calcium carbonate content should never be put in your fish tank no matter how pretty they look. A good example is shale which can contain harmful levels of calcium carbonate.

While fish need a healthy amount of calcium, fossils with high calcium content can easily add too much calcium to your aquarium and cause stress to the fish living in it.

You’ll notice if your fish are stressed if they become lethargic, start swimming erratically, or don’t grow as fast. Too much calcium in your fish tank can even cause your fish to die.

How Much Calcium Do Fish Tanks Need?

If you have corals, coralline algae, and invertebrates in your fish tank, you’ll need to ensure that your tank has about 400 to 420 parts per million (ppm) of dissolved calcium. There are a number of ways to add calcium to your aquarium. Some of the preferred methods include adding eggshells, liquid additives, corals, and cuttlebones.

Where Can You Collect Fossils?

You can collect fossils from anywhere as long as they aren’t near an industrial area. Industrial areas can add harmful chemicals to fossils. While they may not be immediately fatal for your fish, their carcinogenic and harmful effects will lead to their deterioration.
Additionally, you should also make sure you’re not picking up rocks and fossils from an area where it is illegal to do so.

Fossil Care Instructions

Once you’ve determined that a fossil is safe, you should clean it by placing it under running water and scrubbing it with a brush to remove dirt and dust. If your fossil is heavily soiled, you can soak it in a bleach and water solution. Alternatively, you can also boil the fossil for 10 to 20 minutes to kill any unwanted bacteria and parasites. Rocks can stay hot for a long time so make sure to give them sufficient time to cool before handling them.
Between the two methods, boiling your fossil in water is the better alternative since bleach can leak into a rock’s pores and contaminate your fish tank later. Because of this, use bleach as a last resort and only for plastic and glass aquariums.

The Takeaway: Make Sure Your Fossils Are Safe for Your Fish

Fossils are a great way to make your aquarium more beautiful. They’re also great objects that your fish can interact with. However, you’ll want to make sure that the fossils you put in benefit your aquarium without unintentionally harming the life inside it.
By following the instructions outlined here, you can confidently and safely decorate your fish tank with fossils.

Science Talk Doubleheader

Monday August 23, 7 pm

Get ready for Dig With The Experts with two science talks on one night!

First, Executive Director Dr. Phil Stokes presents Britain to Buffalo: The Fossil Connection. His talk will provide an overview of the local rocks and Devonian Period marine fossils found at Penn Dixie. For context, he will discuss the history of geology, Mary Anning, William ‘Strata’ Smith, and their stories connect to the rocks and fossils found in Western New York.

Our second and keynote speaker is Paleontologist Joe ‘PaleoJoe’ Kchodl of Midland, Michigan. PaleoJoe’s talk, Trilobites: Arthropods of the Ancient Seas, will highlight Penn Dixie’s famous fossil — the trilobite — and its cousins from around the world. Learn about the life and death of trilobites and how the Cambrian period became known as the Age of Trilobites.

This is a FREE virtual program thanks to the support of Erie County and the Town of Hamburg. Register here by 6:30 pm on the day of the talk to receive a Zoom invitation. Space is limited to the first 100 participants.

Fossil Hunting for Beginners

New to fossil hunting?

Learn the tricks of the trade from Director of Education & Paleontologist, Dr. Holly Schreiber and/or Director of Science, Catherine Konieczny, M.S. Tour the site and learn all the best spots to hunt for fossils. During this two hour tour we’ll teach you how to find, dig, and preserve all the fossil treasures you find. Bring your own tools or borrow from our limited supply.

No experience necessary. All ages welcome — this program will run rain or shine, dress for the weather.

Dates and times:
Saturdays throughout the season starting at 10 am and lasting until 12 pm.

  • May 15th, 10 am-12  pm
  • June 5th, 10 am-12 pm
  • June 19th, 10 am-12 pm
  • July 3rd, 10 am-12 pm
  • July 17th, 10 am-12 pm
  • August 7th, 10 am-12 pm
  • August 21st, 10 am-12 pm
  • September 4th, 10 am-12 pm
  • October 9th, 10 am-12 pm

Included with admission or FREE for Penn Dixie members.
Select “Fossil Hunting for Beginners” tour-time option when registering online, for no additional charge.

Penn Dixie Claims World Record

Our attempt to set the first-ever GUINNESS WORLD RECORDS™ title for the World’s Largest Fossil Dig on August 25, 2018 is certified. Thanks to 905 fossil diggers who participated, Penn Dixie is now the inaugural record holder for this category! The number one fossil park in the U.S. is now also the official home of the largest fossil dig in the world!! We thank the many community members, partners and business organizations, and media outlets that made this event possible.

“It’s incredible how well things came together for our record attempt. This new recognition cements Penn Dixie’s place in the geologic and paleontologic community, and we’re confident that we can provide an immersive educational and scientific experience, even in our new socially-distanced world.”

Keith Wesolowski, Penn Dixie Director and Chair of the Guinness World Record Event Committee.

The event provided a unique logistical challenge. In addition to being the largest fossil dig attempted by any group on the planet, this event was also the second largest program in Penn Dixie history. We had to recruit and organize dozens of unaffiliated volunteers (stewards) to monitor hundreds of participants. We had to prepare our park for the attempt by designating multiple collection zones and ensuring that all participants would be digging in a coordinated fashion for 30 minutes with proper collecting tools and attire.

Briefing nearly 1,000 participants prior to the attempt was another challenge that we achieved thanks to our enthusiastic volunteers and staff. Following the attempt, we needed to collect specimens from all participants and have them reviewed by unaffiliated professional paleontologists on site to make sure that the fossils were acceptable to the GUINNESS WORLD RECORDS™ review committee.

Participants from the dig are eligible to purchase an official certificate from GUINNESS WORLD RECORDS™ to show that they were part of this record-setting day. Certificates may be purchased here for approximately $28 plus shipping by selecting the date (August 25, 2018) and location (USA) of the attempt. Official certificates may be purchased here.

Our attempt was made possible by Evans Bank, Phillips Lytle LLP, and RP Oak Hill Building Company Inc. Penn Dixie also thanks Erie County and the Town of Hamburg for ongoing support of our organization.

Member Appreciation

Penn Dixie members: Join us from 9 am to 1 pm on Saturday April 24 to kick off the season! Our staff will be on-site to show you what we’ve been up during the offseason. Remember to bring your membership card and ID to show upon check in.

  • Unlimited fossil collecting for all members
  • 1 free (non-member) guest is allowed per cardholder as a thank you for your support
  • Free tool rentals while supplies last
  • Free take home container for your fossils
  • Individually wrapped snacks and light refreshments
  • Complimentary educational tours are available upon request
  • No reservations needed

RSVP Here

Additional non-member guests may pay our normal rate of admission upon arrival with credit card. Guests must be accompanied by a card holding member at all times.

If you would like to stay past 1 pm, please visit out Member Guide at https://penndixie.org/member-guide/