Is it Safe to Reseal A Fish Tank–Is Silicone Sealant Fish Safe

By Jecinta Mwihaki @aquariawise

Can You Reseal Your Fish Tank with Silicone Sealant Safely

You may have an old fish tank in your garage you do not want to toss away, or even one of your functioning tanks has started leaking from the bottom.

So, you wonder!

Is it safe to reseal a fish tank? Will it hold?


It is safe to reseal a leaking fish tank if the leak is not too big and the tank is not very old. Smaller tanks are also easier to reseal because the glass and sealant are not under too much pressure from the water column.

Only reseal and continue using your fish tank if the silicone holds steady and you are sure the tank won’t fall apart once you fill it with water.

If you have to reseal a big part (more quarter the length, width, or height) of your tank, I don’t think it is safe and do not recommend you continue using it.

Maybe even consider converting it into a terrarium or vivarium, or place it in your garage where it will not damage your valuables if it comes apart.

Is Sealant Toxic to Fish

A hundred percent food base silicone sealant with zero additives is the safest fish tank seal for fixing leaks, attaching aquarium rocks work, driftwood, and decorations, and fixing leaks and cracks on aquarium equipment.

Many general-purpose sealants are not safe and can be toxic to fish. Aquarium-safe sealants are often stated as such in their description and name. Fish tank-safe sealing glues sold by brands notable for aquarium accessories, such as Aqueon aquarium silicone sealant, are also often safe.

While choosing the sealant to use in your fish tank, check the packaging to see if it’s useable in an aquarium. Preferably, purchase it from a fish store.

Sealants bought from a general hardware store are mostly general-use and likely toxic to fish.

Is Silicone Sealant Safe for Fish

A hundred percent silicone sealant is safe for fish. Hence, silicone-type seals are common for fixing leaks in aquariums and are available in most fish stores.

The silicone sealant you want should have zero additives, preferably one formulated for use in fish tanks and other wet surfaces. It should also be a waterproof seal that does not shrink.

Go for silicone sealant that dries quickly, albeit not too necessary, if you have plenty of time and are willing to wait for the seal to dry. Most silicone sealants are not aquarium fish safe before they cure.

Is it Safe to Use Hot Glue in A Fish Tank

It is safe to use hot glue in a fish tank. It’s non-toxic. Some brands might contain solvents but no chemicals harmful to tropical fish or aquarium plants.

Even so,…

Hot glue might not hold up underwater and only works well in applications that do not require super adhesion. Use hot glue to make PVC egg traps and aquascapes for your fish, but use pure aquarium-safe silicone on glass.

Aquarium silicone works best for long-term adhesion and creates better seals on aquarium glass. The sealant can handle pressure from the water column best).

Hot glue works best in fish tanks on,…

That said,…

Hot glue is safe for aquarium use, but it helps to exercise caution. Be sure to use a low-temperature glue, and do not let it come into contact with the fish’s skin, gills, or fins. Clean up any excess sealant before placing your pipes or decor in the fish tank to avoid contaminating the water.

If you are using hot glue on aquarium glass, place it before adding water and let it cool before you refill your tank.

You may also want to know the elements in the hot glue you want to use. Ensure the main ingredient is cyanoacrylate because it is not toxic to aquatic life.

What Sealants are Aquarium Fish Safe

A hundred percent silicone sealants with no additives, such as mold prevention, preferably rated for aquarium use on the package, are fish- safe. Sealing glues made by an aquarium accessories brand and sold in a fish store are also more likely to be fish-safe than general-use silicone seals from hardware stores.

If you are in the market for a top-rated aquarium silicone to seal a leak in your fish tank, consider buying one from the table below.

Note that all recommendations are available on Amazon, and Aquariwise will get a small commission for eligible purchases at no extra cost (to you).

Aquarium SealantProsCons
SELSIL Aquarium Silicone Clear Sealant
  • Cures in 24 hours
  • Stong enough for sealing leaking glass and attaching form rocks to the tank bottom
  • 100 percent silicone
  • Non-toxic to fish
  • Easy to use
  • Value for money
  • Does not come with a screw lid for long-term storage after use
  • Seisil adhesive waterproof, and filling properties performs optimally only on wet surfaces
Aquarium SealantProsCons
Aqueon Aquarium Silicone Sealant Clear
  • Ideal for fixing leaks on glass and attaching rocks and wood in an aquarium
  • 100 percent silicone hence non-toxic to fish
  • Good adhesion
  • value for money< li>
  • Reputable aquarium accessories brand
  • Can be tough to squeeze out
  • Takes 24 hours to dry but can take up to 72 hours to fully cure
  • The tube is not too sturdy and might pop open
Aquarium SealantProsCons
Marineland 31003 Silicone Sealant
  • Works well to repair leaks
  • Fish safe
  • Value for money
  • Reputable aquarium accessories brand
  • Curing can take up to 2 days
  • Has a slight irritating smell
  • Can be hard to cure under water
  • The tube does not have an application tube

How Much Silicone Do You Need to Reseal An Aquarium

Depending on the size of the fish tank you want to reseal and the extent of the leak, you will need anywhere from a single 100 ml silicone tube to around 4 or 5, 300 ml tubes to reseal an aquarium.

Four 300 ml silicone sealant tubes are enough to sufficiently seal an old leaky 150-gallon fish tank.

To ensure you do not use more silicone than is necessary, remove the old seal, clean the area carefully, and ensure it is dry before you add the new seal.

You can remove the old sealant using a utility blade flat against the glass, then clean the area with isopropyl alcohol. Let it sit overnight, rinse to remove the alcohol, then place the new silicone seal once the area is completely dried.

Apply the new sealant and let it sit for 24 to 72 hours, then test the tank. Ensure the leaks are sufficiently sealed before adding water and fish to the tank.

How Often Should You Reseal Your Fish Tank

While there is no definitive answer to the question of- how often you should reseal your fish tank- it is generally recommended that you do so every few years (between 5 and 10). This will ensure the integrity of your aquarium and the well-being of your fish.

If you have a newer fish tank, you may not need to reseal it as often as older tanks, as they are typically made with better materials that are less likely to leak.

However, even with a newer tank, it is still essential to check for leaks and to reseal the tank if necessary.

If your tank is leaking, fix it as soon as possible. Not only will this protect your fish, but it will stop your fish tank from losing its structural integrity and cracking open.

If you are unable to fix the leak yourself, you may need to call in a professional to do so or purchase another tank.

How Do You Tell If an Aquarium Needs to Be Resealed

One question that often arises for aquarium owners is whether or not their tank needs to be resealed. There are a few key signs that can help you make this determination.


If the tank is leaking, it definitely needs to be resealed. You can check for leaks by looking for water on the floor around the tank or by checking the water level in the tank. If the water level is falling, there is a good chance that the tank is leaking.

Your aquarium filter may also leak, so investigate a leak to be sure water is seeping from the tank.


If your aquarium glass is bowing, your fish tank needs resealing and a brace to keep it from cracking. Once you notice the bow, check the trims and seals to ensure they are not leaking.

Glass tanks have a certain tolerance for bowing when filled with water and should not be a concern or a reason to reseal your tank if it is not apparent to the eye.

However, look out for advanced signs and reseal your tank if the bowing gets worse or if the tank starts leaking.


Bows and leaks are more frequent in older tanks (than in newer tanks), so if you have an old tank, you should know it will need to be resealed after a few years.

Can You Put New Sealant Over Old Aquarium Glass

Yes, you can put new sealant over old aquarium glass. If the old silicone is in good condition and has not cracked, it is probably best to leave it in place, but if the old sealant is peeling or has cracks, you will need to remove and replace it.

You may also want to replace the sealant on old leaking aquarium glass since it’s cheaper than purchasing a new tank.

Be sure to use a sealant designed for aquariums, as regular silicone may not be safe for fish and other aquatic creatures.

Remove all of the old seals before adding the new silicone coat to ensure you get optimal adhesion.

Is it Easy to Reseal A Fish Tank

It’s not as easy as it seems to reseal a fish tank. I’ve tried it before, and it was a huge mess. It is also time-consuming but cheaper than buying a new tank. It should not cost you more than 50 dollars to reseal your fish tank (yourself). You will need aquarium-grade silicone with super adhesion if you want the tank glass to stay together once you reseal it.

You will also need to remove the old sealant with a razor blade scraper for the new seal to hold.

The sealant won’t stick to the glass, and when you try to clean it up, it will create a bigger mess if you fail to remove the old sealant or clean the glass properly.

Once you finish resealing your fish tank, you will also need to wait for the silicone to dry before you can add water to the fish tank, and if the tank still leaks you don’t have a choice but to empty it and seal the tank some more.

So, if you are not sure you are up to the task, it is best to consult a professional. They can help you determine whether your fish tank needs to be resealed and guide you on how to do it.

Most will even reseal the tank for you for a fraction of the cost of buying a new fish tank.

How Much Does Resealing A Fish Tank Cost

If you reseal a fish tank on your own, it will cost you under 50 dollars because there is no labor cost incurred. Silicone sealant will cost you between 20 and 30 dollars, 13 dollars for a razor blade scraper, and 5 dollars for painter’s tape. You will also need to buy pure acetone and a caulk gun if you do not have them in your house.

If you decide to get a professional or staff from your local fish store to reseal the fish tank for you, it may cost a little more than 90 dollars for the whole job depending on labor cost in your state or country.

You might get a bargain if you go to the fish store you get your supplies, especially if you are making a purchase😎😉 on that day.

Thank me later!

Can You Seal A Fish Tank with Water in it

You can reseal a small leak in a fish tank with water (in it) from the outside, but note this is not a solid solution. If the seal does not hold, you must empty the tank and reseal it properly.

To reseal the fish tank, reduce the water to a lower level than the leaking spot on the glass, then apply aquarium-safe silicon on that part. Refill the tank halfway to check if the leak has stopped (and whether the seal will hold) before you fill it to the brim.

If the leaking part is on the lower level of the fish tank, you can only seal it from the outside, but for a leak toward the top, reduce the water level and seal it on both sides.

Please note…

Sealing a fish tank with water is only possible for small leaks. If your aquarium is leaking water to substantially soak the stand, you must empty it and seal it inside and outside.

That’s all for this post. We hope we’ve adequately answered your query.

See catch-up on the next post.

← All articles

The Aquarium Club ↓

Join the 37k+ strong aquarium community

The AquariaWise Newsletter is known for cutting through the noisy world of pet fish keeping showcasing stunningly breathtaking aquarium fish and superbly insightful aquarium plants to help you bring out the peace and serenity you seek with your aquariums. And it doesn't stop there... think aquarium fish care, plant care, building fish tanks, everything aquariums... you'll be right at home.