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Best Aquarium Safe Silicone & How To Use It

Of all the aquarium products out there and substances that go into building our setup, the silicone glue holding everything together is something most of us rarely think about.

This modern miracle molecule can resist pressure and temperature extremes while being durable, flexible, and inexpensive all at once! What is aquarium safe silicone and why should we have some on hand at all times?

What is Silicone Gel?

Silicone is a special substance that has so many useful properties that it’s an everyday miracle molecule. Silicone is a polymer (an especially large molecule) containing silicon, oxygen, carbon, and hydrogen.

By structuring these polymers in specific ways, we can get a gel that has a wide variety of uses. Like its more familiar elemental group relative, Carbon, Silicon can combine in an endless array of shapes that give it an astounding chemical diversity.

As a result, there are forms of Silicone gel that are heat resistant up to 300℃ (572℉), waterproof, continually sticky, or even sticky only when pressure is applied. Silicone and its related forms are used in breast implants, bakeware, clothes, medical devices – and aquariums!

Why Can’t I Use Regular Silicone?

Household silicone caulking or sealant is often less expensive than aquarium-safe silicone and you often get more of it. So why not simply use this?

The problem with household brands is that their intended use means they aren’t necessarily fish-safe. Regular silicone is often adulterated with anti-molding agents that are ideal for a household project – but toxic to fish and plants. These chemicals will leach into the water over time, potentially causing problems.

Aqueon Silicone Sealant, 1-Ounce, Clear
  • Waterproof seal stops leaks
  • Permanently flexible; does not crack or shrink
  • Easy to apply long-lasting bond

Non-aquarium safe silicone may also release chemical fumes while curing and even for some time after if submerged. These fumes may be harmless in air or the spacious confines of a home or the outdoors. But again, there are too many unknowns when dealing with the hundreds of varieties of household silicone types.

There’s no good reason to be using regular silicone to gamble on the lives of your fish and plants, which cost far more than what you’d save using that leftover silicone in your garage. Especially when aquarium safe silicone is available so readily and inexpensively.

Aquarium 100% Silicone Sealant (10.4 fl oz) Non Toxic Safe for Fish
  • 100% Silicone - Apel’s aquarium sealant is...
  • Multipurpose - When it comes to your aquarium, our...
  • Strong Bond - The fish tank glue for glass is very...

Aquarium safe silicone is formulated to cure in air so it should be kept as dry as possible. Most formulas take 24-48 hours to cure, at which point water can be added to the fish tank. However some brands, like Apel, use formulas that can cure in as little as two hours – perfect for a sudden repair need or day project!

When still drying, aquarium safe silicone is tacky and easily shaped. Once dried the substance becomes rubbery and retains the slight salt and vinegar chips aroma that it has while curing.

Despite being so seemingly fragile aquarium silicone can resist the immense pressures water exerts on aquarium glass for decades. It’s nearly entirely chemically inert and resistant to corrosion.

Seachem Flourish Glue
  • Performance driven at affordable prices
  • Made in the USA with quality materials
  • Field tested to ensure nothing but the best for...

Being pale to colorless, silicone gel would be an ideal glue for plants, rocks, and wet decorations in your aquarium. Unfortunately, it does not cure while wet. For that, you need fish-safe superglue, like Seachem Flourish Glue.

While it does dry into a noticeable white color, when used sparingly it creates a permanent bond to wet surfaces and is also 100% fish and plant safe!

Uses for Aquarium Safe Silicone

Here are a few common uses for silicone:

Aquarium Construction

Most of us fish-keepers buy our aquariums and fill them right up with livestock and decorations. But what if you want to customize your setup? In order to add tiers, shelves, secure spray foam backgrounds, and other upgrades, you’ll need aquarium safe silicone on hand at all times.

A line of silicone is enough to provide a secure platform for nearly any DIY aquarium construction project!

Marineland 31003 Silicone Squeeze Tube, 2.8-Ounce, 85.05-Gram
  • Squeeze tube
  • Make sure area is dry before use
  • 3-Ounce

If you need to use more silicone than usual, such as when sealing the inside of a custom aquarium hundreds of gallons in size, be advised that it may take longer than expected for all of that silicone to cure.

You don’t want to rush to fill the aquarium as it may be insufficiently cured inside and simply blow apart from the pressure! Wait days or even a couple of weeks as needed to allow your silicone to fully cure for large-scale projects.

Sudden Leaks

Aquarium safe silicone is also essential for leaks that arise. Any aquarist who has a tank for a decade or more may run into this dreaded issue. While silicone is mostly chemically inert, UV degradation from high-power saltwater lights, stray chemical reactions, and abrasion from a lifetime of use may wear away at the coating.

Fortunately, by having silicone on hand, you can immediately treat the issue. Ideally, you’ll want fast-curing silicone on hand to get your fish back into the aquarium as soon as possible.

If you’re a fan of buying used aquariums on Craigslist, at garage sales, or other well-used outlets I strongly recommend keeping silicone on hand. You may not realize you have a leaker until you get home with your bargain and try to fill the aquarium.

Even if the owner patched the tank themselves with silicone before selling it, they may not have done as good a job as they think they did. Always be prepared when buying discount tanks!

Often, the owner patching up their tank for resale won’t remove the old silicone seal, which is a problem waiting to happen. Simply patching over the leak location with new silicone may not completely fill any microtears in the older material. There’s a good chance water forces its way around the silicone band-aid, ensuring your “new” tank leaks again right in the same spot!

For some projects you may want to color-match your silicone to the surface. For instance, when repairing a black pond liner, a patch of standard whitish blue silicone may be too obvious in the right light.

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For these instances black silicone is a much better purchase! Just beware of the fumes with this particular brand; they are much more irritating than standard silicone. If working indoors, make sure you have open windows and fans to prevent the gases from building up.

Aquarium DIY Projects

If you’re a fan of upgrading your setup in any way, aquarium silicone is essential to have on hand. Besides the aquarium itself, I’ve used silicone for DIY carbon dioxide reactors for live plants. It can also be used to secure additional LED light strips into a hood for nano setups.


Aquarium safe silicone seems like a niche product at first. In reality, it’s a product you never need until it’s absolutely essential that you have some right away! So it’s much better to have a tube tucked away at all times for the eventual repair or creative construction issue, wouldn’t you agree?

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

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