Will Acrylic Paint Wash Off if Used Inside an Aquarium?

One of my neighbors bought a new aquarium last month. She gathered a few stunningly beautiful pieces of driftwood and stones to put inside with fish. But before putting them inside the aquarium, she wanted to color them beautifully.

She called me and asked if she could color them with acrylic paints, which she already had in her home. Will the paint stay there? Is it waterproof enough, and if not, what can she use to make the paint waterproof?

She had many questions, 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…

Does Acrylic Paint Wash-Off with Water?

Acrylic paints aren’t 100% waterproof. 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 are using warm water in your aquarium (which you must be in winter).

So, if you want to use acrylic paint in your aquarium, you will need a waterproofing sealer to make it work.

How Safe is Acrylic Paint On the Fish Tank?

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 polymer chains are formed by the reaction of an acrylic monomer and a polymeric material. 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.

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. The advantages of using acrylic paint in an aquarium are:

• It’s easy to find, cheap, and non-toxic
• It can be easily removed if you don’t like the way it looks
• It’s vibrant and can add a beautiful pop of color to your aquarium decorations submerged in water

You can use the paint on plastic, stones, rocks, fabrics, and even on the inside of the aquarium glass surface to decorate your fish tank beautifully.

But as I just said, the paint (even when it’s dried) will gradually flake off whatever they are painted on.

The harmful chemicals sometimes produced by the leaching of paint in the water can be hazardous for your fish and other aquatic creatures. This means, even though the paint was initially non-toxic, the flaked pieces of paint that break apart can be poisonous to some fish if they view it as food and consume it.

So, what can you do to make the paint stay on the aquarium decorations and not flake off? Just, prepare the aquarium surface well before painting and use a waterproofing sealer after you paint.

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Using Acrylic Paint to Paint Aquarium Decorations

If you decided to use acrylic paint to add color to your aquarium tank and 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 old newspaper to make cleanup more effortless if you accidentally spill or drip some paint.

Step 2. Clean Aquarium and Decorations

Clean the surface of the 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 Surface

If you are painting with a light color over a dark one, or you are painting 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, roller, or spray can, following the manufacturer’s instructions.

Step 4. Choose Your Paint Colors

Now, it’s time to choose the colors of aquarium-safe acrylic paint you want to use. You can use a single color or mix different colors to create unique shades on the pieces of rocks and toys you will be using in a fish tank.

Step 5. Paint the Aquarium

Once you have chosen the colors, it’s time to start painting the objects with fish-safe paint.

Using a paintbrush or a sponge apply the thin layers of paint to the larger areas first and then move on to the smaller ones. Thicker layers will take much time to dry, so avoid coating the rocks and reefs with thick paint layers.

Step 6. Let it Dry, and Apply Additional Coat

Let the acrylic paint layer dry to the touch which usually takes about 30 to 40 minutes. If you want, you can use a hairdryer to speed up the process by blowing warm air over the painted surfaces.

Once the first layer of paint is dry, apply an additional layer letting the first layer dry completely before proceeding to the next coat.

Step 7. Apply a Final Top Coat of Paint to the Objects

To make the paint more resistant to peeling and prevent the color from fading, evenly apply a final topcoat of acrylic paint to the painted surfaces.

Once coated, allow the aquarium decorations to dry and cure completely for about 48 hours. Usually, it takes 24 hours to cure the acrylic paint, but since you will be submerging the painted objects in the water, I would recommend waiting at least 48 hours to be on the safe side.

TIP: 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.

Sealing and Waterproofing Acrylic Painted Aquarium and Objects

A waterproofing sealer varnish on the fish tank ornaments will help make your paint job last longer by holding the paint onto the surface and making it more resistant to water.

You can find many waterproofing sealers in the market for interior and exterior use, but ensure you get the one that is safe for aquariums. Some of the most popular brands that make aquarium-safe waterproofing sealers are Plasti Dip and Krylon Fusion.

I had worked with Krylon Fusion All-In-One Spray before and recommended the same to my neighbor for sealing her fish tank decorations that, included rocks, fake plants, and plastic toys.

Krylon Fusion is aquarium safe (above and below the waterline), but it isn’t as good to hold on to the glass of fish tanks. So if you want to use a sealer for aquarium background glass (from the inside), you can use a Plasti Dip.

Once you have your waterproofing sealer ready, you can apply it by following these steps…

• Using a spray-on sealer or brush-on sealer, apply an even coat to the painted areas.
• Let the waterproofing sealer dry entirely according to the manufacturer’s instructions.
• After it has dried and cured, you can submerge the decorated rocks or toys in your aquarium.

Related FAQs

Which paint can I use for the cement fish tanks?

Cement fish tanks are standard in many homes. I think two-part epoxy resins that dry clear are best for painting cement fish tanks or concrete outdoor aquariums.

You can find these types of resins at most hardware stores or online. When buying ensure that the resin is non-toxic and safe for your aquariums before using it.

Can acrylic paint inside the aquarium kill my fish?

Acrylic paint will not kill fish and other aquatic animals unless they consume it. So, to keep your aquatic animals safe I would recommend not using paint inside the aquarium. If you are using, get premium quality, non-toxic acrylic paints and sealers that are fish safe.

How do I remove acrylic paint from my aquarium glass?

If you want to remove the paint from your aquarium glass or expensive decorative objects, you can do so by using a razor blade or a putty knife. First, scrape off most of the paint and then use a glass cleaner to remove the remaining paint.

The bottom line

Painting inside the aquarium and the decorative objects you put inside is a fun project that can be completed on the weekend with your kids.

Just make sure that you use non-toxic and safe materials like acrylic paints that won’t harm your aquatic animals. Also, ensure the objects are correctly sealed to make the paint waterproof when you submerge them in an aquarium.