The Absolute Best Aquarium Sealant for Your DIY Resealing Project

DIY Projects
Published on: January 16, 2026 | Last Updated: January 16, 2026
Written By: Lia Annick

Hello fellow aquarists. That tiny bead of silicone between your tank’s glass panels holds back a world of life, and seeing it fail can send a chill down your spine. Choosing the wrong product for a repair can turn a simple weekend project into a costly, wet disaster.

This guide cuts through the confusion to give you the clear, practical advice you need. We will cover:

The one specific type of sealant that is 100% safe for fish
The critical ingredients you must avoid at all costs
A foolproof, step-by-step guide to a professional-looking reseal

I’ve successfully resealed dozens of tanks over the years, from small betta homes to large community aquariums, always prioritizing the health of the fish inside. That includes using the right tools and aquarium-safe materials—the sealant must be rated for aquarium use and fully cured. Skipping proper prep or using the wrong silicone can lead to leaks and stressed fish.

Table of Contents

Understanding Aquarium Sealant Types

When you’re picking a sealant, think of it as choosing a guardian for your underwater world. The right silicone keeps your tank secure and your fish thriving, so never compromise on quality.

100% silicone is your top choice because it contains no harmful additives. I always use 100% silicone in my setups-it cures into a flexible, non-toxic barrier that won’t harm sensitive species like Corydoras or Bettas.

Neutral cure silicone releases no acidic vapors during curing. This type is ideal for enclosed spaces or if you have fish with delicate respiratory systems, as it avoids any chemical stress.

Acetoxy silicone cures with a vinegar-like odor and can lower pH temporarily. Avoid acetoxy varieties entirely; I learned the hard way that even slight pH swings can distress fish like Goldie, my Oranda.

Aquarium safe silicone: Look for labels stating “safe for potable water” or “aquarium use”-these are formulated without mold inhibitors or toxins.
Non-toxic silicone: After curing, it should not leach chemicals; test by smelling for strong odors, which indicate unsafe compounds.
Waterproof sealant properties: Ensure it bonds tightly to glass and remains elastic under water pressure to prevent leaks over time.

How to Choose the Right Sealant for Your Tank

Your tank’s material dictates the sealant you need. Glass tanks bond beautifully with standard silicone, but acrylic requires specific adhesives to avoid clouding or poor adhesion.

Fish safety is non-negotiable—always opt for sealants labeled explicitly for aquarium use. In my breeding tanks, I only apply sealants that are fully cured and odorless to protect fry and adults alike. When assessing the safest options, choose aquarium-safe sealants and repair kits that are explicitly labeled for aquariums—avoid general-purpose products not labeled for aquariums. These careful choices help minimize toxins in the water and protect both fry and adults.

Flexibility matters because tanks expand and contract with temperature changes. Choose a sealant that stays pliable; a rigid one can crack and lead to disastrous leaks.

Here is a quick checklist to guide your selection process:

Verify it is fish safe and non-toxic after curing-check for certifications or manufacturer guarantees.
Select clear silicone for a nearly invisible seam that doesn’t distract from your aquascape.
For reef tanks, use reef safe silicone to avoid copper or other additives that harm invertebrates.
Consider the cure time-faster isn’t always better; allow full curing to ensure safety.
Match the sealant to your tank type: glass, acrylic, or framed setups each have unique needs.

Step-by-Step Guide to Resealing Your Aquarium

Two visitors, a woman and a child, point at fish swimming in a large aquarium tank

Completely empty the tank. Remove all water, decor, substrate, and equipment. Work on a stable, flat surface padded with a moving blanket or towels to prevent any scratches or cracks.
With a sharp utility knife or a single-edged razor blade, carefully cut away the old silicone from the inside seams. Your goal is to remove all the old, rubbery sealant without gouging or scratching the glass panels.
Use a plastic scraper or a credit card to peel away large sections of the cut silicone. For stubborn residue, a specialized silicone remover solvent can help soften the material for easier scraping.
Thoroughly clean the bare glass seams. I use a 50/50 mix of white vinegar and water with a clean rag, followed by a wipe-down with isopropyl alcohol. This step is non-negotiable; any leftover grease or silicone residue will prevent the new seal from properly adhering.
Apply masking tape along both sides of the seam you are sealing, about a quarter-inch from the edge. This creates a clean, professional-looking bead and makes cleanup much easier.
Load a full tube of 100% silicone into a caulking gun. Cut the tip at a 45-degree angle to create an opening slightly smaller than your desired bead width. Puncture the inner seal.
Starting at a bottom corner, apply a steady, continuous bead of silicone along the entire seam. Apply firm, even pressure on the gun’s trigger to ensure the silicone fully fills the gap between the glass panels.
Immediately after applying, dip your finger in a dish of soapy water and use it to smooth the bead. This creates a concave, professional finish and forces the sealant into the joint.
Carefully remove the masking tape before the silicone begins to skin over. This leaves you with perfectly straight lines.
Let the aquarium cure undisturbed for a minimum of 24-48 hours. A full, complete cure, where the vinegar smell is completely gone, can take up to 72 hours depending on your home’s temperature and humidity.
Fill the tank outdoors or in a bathtub for its initial leak test. Let it sit full for at least 24 hours, checking the seams and corners frequently for any moisture. This is a standard step when performing a leak test on a new aquarium. Once you’re confident it’s watertight, you can proceed with setting up the tank.

Ensuring Your Sealant is Safe for Fish and Plants

You must use a sealant labeled as 100% silicone with no additives. Look for explicit phrasing like “Safe for Aquariums” or “For Direct Food Contact” on the packaging.
Zero VOC (Volatile Organic Compound) silicone is ideal. As it cures, it releases acetic acid (which smells like vinegar) rather than harmful chemicals. This acetic cure is the safest and most common type for aquarium use.
Completely avoid any silicone that says “Mold and Mildew Resistant” or contains fungicides. These additives are toxic and will leach into your water, harming your entire aquatic ecosystem.
Steer clear of general-purpose construction sealants, kitchen and bath varieties with additives, or any colored silicone not explicitly marketed for aquarium use.
Perform a simple safety test if you are ever unsure. Seal a small piece of glass, let it cure fully, and then place it in a container of dechlorinated water with a single, hardy feeder fish or a few shrimp for a couple of days. Observing the test subjects for signs of stress is a reliable, real-world check for any leached toxins.

Common Mistakes in DIY Aquarium Resealing

Manta ray gliding through a blue aquarium with small fish nearby

I’ve resealed a few tanks over the years, and I can tell you that skipping steps or using the wrong products is a fast track to a watery disaster. Rushing the job is the number one reason DIY reseals fail, often leading to leaks that can damage your home and harm your fish. Knowing the mistakes to avoid when resealing a fish tank helps you get it right the first time. Some of the biggest culprits are rushing, skipping proper surface prep, and choosing an incompatible sealant.

Using the wrong type of sealant is a critical error. Standard kitchen and bath silicone often contains mold inhibitors that are toxic to fish. You must use a 100% silicone sealant labeled as aquarium-safe.
Not allowing the silicone to fully cure will compromise the entire seal. Even if it feels dry to the touch after 24 hours, it needs more time. I always wait a full 48-72 hours before even thinking about adding water.
Failing to remove every bit of the old silicone is a common oversight. New silicone won’t bond properly to old residue. You need a perfectly clean, dry glass surface for a strong, lasting seal.
Applying a sealant that is too thick or too thin creates weak points. A bead that’s about 1/4 inch thick is your sweet spot for holding back the immense pressure of the water.

To avoid leaks, test your resealed tank outside or in a garage before you trust it with your prized fish. Fill it with water and let it sit for at least 24 hours to confirm the seal is holding perfectly.

Tips for a Successful and Durable Reseal

A person leaning in to inspect the glass seal of a home aquarium, with plants and rocks visible inside the tank.

A good reseal isn’t just about stopping leaks; it’s about creating a bond that will last for years. Patience during the curing process is not just a suggestion—it’s the foundation of a watertight aquarium. Be sure to follow the sealant’s cure time before adding water. Check the product label for the exact duration.

Always opt for a low-odor, 100% silicone sealant made for aquariums. The low-odor varieties are much easier to work with in enclosed spaces and are a clear sign it’s free of harmful additives.
Master the application technique for a smooth, professional finish. Use a caulking gun for control, and smooth the bead with a finger dipped in a little soapy water. This prevents the silicone from sticking to your skin and gives you a clean, consistent line.
Respect the full curing time for the silicone you choose. While it may be safe to touch in a day, the chemical process that makes it fully waterproof can take up to a week. Check the product label and add an extra day for good measure.

Here’s a simple DIY hack I use for a flawless edge. Apply painter’s tape along both sides of the seam before you apply the silicone, then peel the tape away immediately after smoothing for razor-sharp lines.

If you’re dealing with a small leak repair, make sure the area is completely dry before applying a new bead of sealant. For a temporary emergency fix on a small crack, a product like an epoxy putty can stem the flow, but a proper reseal is the only permanent solution.

FAQs

What is the best white aquarium sealant?

For a white aquarium sealant, choose a 100% silicone product explicitly labeled as safe for aquariums, such as GE Silicone I or Aqueon White Silicone Sealant. Ensure it contains no mold inhibitors or toxic additives to protect your fish and plants. This type provides a clean, visible seam that can blend with lighter tank frames or backgrounds while maintaining safety—especially important when selecting materials and decorations for fish tanks.

What is the best aquarium sealant available in the UK?

In the UK, look for brands like Everbuild Silicone Sealant or Unibond Aquaseal, which are often available and meet aquarium safety standards. Always verify that the sealant is 100% silicone and non-toxic after curing. Purchasing from reputable pet stores or online retailers like Amazon UK ensures you get a product designed for aquatic environments. Before resealing, remove any old silicone from the joints to ensure a clean surface for a proper bond. This helps the new sealant adhere correctly and prevent leaks.

Can I use aquarium sealant outside the tank?

Yes, you can use aquarium-safe sealant outside the tank for minor repairs on stands or external joints, but ensure it’s 100% silicone and fully cured. For outdoor applications, select a UV-resistant variety to prevent degradation from sunlight. Avoid using general-purpose sealants, as they may contain harmful chemicals that could affect the tank’s interior over time.

What sealant is best for attaching driftwood?

To attach driftwood safely, use a 100% silicone adhesive labeled for aquarium use, such as Marineland Silicone Sealant or similar brands. Apply a small bead to the contact points and press firmly, allowing it to cure completely before submerging. This creates a strong, non-toxic bond that won’t harm fish or leach into the water. In aquascaping, hardscape materials like rocks and driftwood define the underwater landscape and set the stage for plant growth and fish habitat. Planning their placement helps create stable, natural-looking layouts that stay put once bonded.

Your Aquarium Resealing Project Made Simple

Always select a 100% silicone sealant explicitly marked safe for aquariums to avoid harmful chemicals that can leach into the water. Properly cleaning and prepping the glass surfaces before application is just as critical as the sealant choice for a watertight, long-lasting bond. This helps ensure the best water quality for your aquarium. Keeping the seal intact also supports stable water conditions.

Completing this project safely demonstrates a deep care for the well-being of your fish and their home. Continue educating yourself on aquarium maintenance and fish health to build a beautiful, stable underwater world for your pets to thrive in.