Painting Inside an Aquarium – What Paint to Use?

Last week, one of my neighbors gathered a few stunningly beautiful pieces of driftwood and stones to put inside her old aquarium.

But she wanted to color them beautifully before putting them inside the aquarium. She also wanted to paint the backside of the fish tank so that it would create an illusion of an underwater landscape.

She called me and asked about the type of waterproof paint that’s 100% safe to use for fish and can stay there for a long time, and what steps she should follow to make the paint last longer.

She actually had many questions in mind, and I thought to jump in and write a detailed post of what I advised her.

Hopefully, it can help many users who want to know about aquarium-safe paint for decorations. So, let me start with the main question first…

Why You Might Need to Paint Inside an Aquarium?

Painting the inside of an aquarium isn’t just about making it look pretty—it’s about function meeting flair.

A painted interior helps hide cables, filters, and that less-than-glamorous equipment jungle, creating a clean, immersive backdrop that enhances your fish’s colors.

Technically, it also reduces glare and visual stress for aquatic life, promoting a calmer environment. If done right (with aquarium-safe, non-toxic paint), it prevents algae from clinging too easily to glass surfaces.

So yes, it’s part art, part science—a touch of creativity that makes both you and your underwater residents a little happier.

Best Paints for Inside Back of Fish Tank

Painting the back (or interior) of a fish tank can give a clean, finished look — but there are very important differences in what’s safe depending on the material of the tank (glass vs. cement/concrete) and whether you’re painting inside (water-contact) vs. only the back side (outside water).

Below is a breakdown of things to consider + recommended paints + cautions.

1- Paint for glass tanks back

Back panel (outside water) is the easiest, safest scenario. Cleaning the glass well, masking off parts you don’t want painted, using a good adhesive paint or spray paint meant for glass/plastic, then curing thoroughly.

Many aquarists use acrylic craft paint or spray paint on the outside back of indoor glass aquariums.

Water-based acrylic or latex paints (for walls) are generally considered among the safest for painting surfaces that will not be submerged, particularly if they are specifically labeled as aquarium-safe.

The water-based and fast-drying nature of latex and acrylic paints also means they are less likely to release harmful volatile organic compounds (VOCs).

Moreover, these are free from harmful chemicals that might leach into the water and harm fish, invertebrates, or plants, making them suitable for use in aquatic environments.

However, keep in mind that not all acrylic paints are suitable for aquarium use, as some might contain harmful pigments. So it’s essential to carefully research the brand before buying.

2- Paint for interior submerged glass tank

This is much riskier because the paint is in contact with the water and may leach. Many sources caution against it unless using a genuine aquarium-safe coating.

Moreover, the paint, even when it’s dried, will gradually flake off whatever they are painted on. This also means that even though the paint was initially non-toxic, the flaked pieces of paint that break apart can be hazardous to some fish if they view it as food and consume it.

If you must paint inside a glass tank, choose an epoxy paint or coating rated for submersion, and follow very strict curing procedures.

3- Paints for outdoor cement or concrete fish tanks

If the tank or background is cement, concrete, or masonry (e.g., a basement pool converted to a fish tank, or a pond-style cement aquarium), the requirements are different.

If you have these concrete outdoor aquariums and plan to refinish their cement-based backgrounds, non-toxic two-part epoxy resins that dry clear are best for them.

Fish-safe, non-toxic, and waterproof epoxy coating, such as a pond-safe epoxy or a solvent-free epoxy paint, is also the best option for the inside of a cemented fish tank.

However, if you want to use a paint like acrylic, it must be completely sealed with an aquarium-safe clear epoxy resin.

In general, cement/concrete surfaces are porous, can absorb water, have cracks/voids, and may leach lime/alkali or other compounds.

So, you need a coating/seal that is waterproof, inert, and suitable for underwater exposure. A water-based wall paint or regular Rustoleum enamel paint is not sufficient if it will be submerged or in constant contact with water.

Steps for Using Acrylic Paint for Aquarium Decorations

Acrylic paint is a fast-drying water-based paint made of pigment suspended in acrylic polymer emulsion (a cross-linked network of interconnected polymer chains dispersed in water).

The water evaporates when the acrylic paint dries, and the acrylic polymer chains interlock to form a solid film. That’s the reason acrylic paints are water-soluble but become water-resistant when it dries.

If you decided to use acrylic paint to add color to your aquarium tank and on decorations like reef and driftwood, here are the steps you need to follow:

Step 1. Prepare the work area

Start by covering the floor around your work area with a drop cloth or some old newspapers to make cleanup more effortless if you accidentally spill or drip some paint.

Position your empty aquarium on a protected surface and set aside all decorations for cleaning.

Step 2. Clean the aquarium and decorations

Begin by wiping the back surface of the tank with a soft sponge or cloth to eliminate dust and algae. Steer clear of harsh chemicals to prevent potential harm to the fish.

Rinse the sponge with warm water and proceed to clean the sides and bottom of the tank. Pay close attention to corners and crevices, where grime tends to build up. Once you’ve thoroughly cleaned the tank, rinse it with fresh water to remove any remaining residue.

Next clean decorative aquarium pieces (you intend to paint) with soap and water to remove any dirt, dust, or grease. Pieces like driftwood can have algae and other growths on them that need to be scrubbed off before painting.

So, clean and disinfect them nicely using a bleach solution, vinegar, or soda water. After cleaning, rinse the pieces and allow them to dry completely.

Step 3. Prime the surfaces

If you plan to paint with a light color over a dark one, or on surfaces like plastic or glass, you will need to prime the surface first. This step is necessary to improve the acrylic paint’s adhesion to the surface and prevent peeling.

For priming, you can use an acrylic-based primer or white latex paint. Apply the primer using a brush, mini roller, or spray can, following the manufacturer’s instructions.

Step 4. Paint the aquarium and decorations

Now, it’s time to select the aquarium-safe acrylic paints you wish to use – opt for a single color or blend different hues to create unique shades for the rocks and toys you’ll place in the fish tank.

Use a paintbrush or sponge to apply thin layers of fish-safe paint, starting with the larger areas and gradually moving to the smaller details. Avoid applying thicker layers, as they take longer to dry and can flake off faster.

Step 5. Let the paint dry, and apply additional coats

Allow the acrylic paint to dry, which typically takes around 30 to 40 minutes. To speed up this process, you can use a hairdryer, gently blowing warm air over the painted surfaces.

Once the first layer has dried, apply another coat as you did previously. For added durability and to prevent fading or peeling, apply a thin final topcoat of acrylic paint evenly across the surfaces; let the decorations dry and cure for at least 48 hours.

Acrylic paint generally cures within 24 hours, but I recommend waiting 48 hours to ensure the objects are fully ready for submersion in water.

Additional Tips and Ideas

To make your stones or other objects more beautiful, you can sketch or print out images you like on paper, cut them out, and then use them as a stencil to paint over.

Use an airbrush to paint your aquarium decorations and make them beautiful. This technique allows you to achieve intricate details and subtle gradients that can enhance the overall appearance of your objects.

For airbrushing make sure you use a proper thinning medium (Liquitex Professional Airbrush Thinner) for optimal airflow of paint through the airbrush.

While spraying, hold the airbrush at a consistent distance from the surface to avoid pooling or drips.

Where Can You Use the Acrylic Paint Inside the Aquarium?

Acrylic paint can adhere well to clean and primed glass surfaces, commonly used on the aquarium’s back wall for decorative purposes.

But inside the aquarium, you can use this paint on several other surfaces, such as:

• PVC pipes or structures used in custom aquarium setups
• Ceramic decorations, like hiding caves or plant pots
• Artificial rocks, plants, or ornaments made of plastic and wood

Depending on how much the paint is diluted (with water) or how thickly it is applied, the finished product can range from very soft to very hard.

Also, acrylic paints aren’t 100% waterproof. This means that although water-resistant (after they are dried and have stuck to your painting surface), they can still be washed off if exposed to water for a long.

The wet paint will be more likely to bleed and run fast, especially when you use warm water in your aquarium (which you must do in winter).

So, what can be done to make the paint stay on the aquarium decorations for long without getting washed or flaked off? Let’s explore further.

How to Seal and Waterproof the Acrylic Painted Objects Inside Fish Tank?

Applying a waterproofing sealer varnish on the painted fish tank ornaments will maintain their vibrant colors over time and protect the paint from water damage, fading, and peeling.

This type of finish also ensures that no harmful chemicals leach into the water, which could jeopardize the health of your fish and other inhabitants in the aquarium.

You can find many aquarium-safe waterproofing sealers in the market for interior and exterior use, but the most popular brands I have tried are Plasti Dip and Krylon Fusion.

Krylon Fusion All-In-One Spray is safe for fish tank decorations such as rocks, fake plants, and plastic toys (above and below the waterline), but it isn’t as good at holding on to the glass.

So if you want to use a sealer for aquarium background glass (from the inside), you can use Plasti Dip.

The bottom line

Painting inside an aquarium isn’t just about aesthetics—it’s about safety and longevity. The key is to choose a paint that’s non-toxic, fully waterproof, and completely cured before water contact.

For glass tanks, it’s far safer to paint the outside back panel using water-based acrylics or enamel sprays like Rust-Oleum—they deliver clean results without risking your fish.

For cement or concrete tanks, only epoxy coatings or aquarium-safe waterproof paints should ever touch the water.

Always give the paint ample curing time—patience here can mean the difference between a thriving tank and a toxic disaster.

When in doubt, remember: if it’s not explicitly rated for underwater use, keep it outside the tank. A perfectly painted aquarium should enhance your setup—not endanger it.