Can You Use Potting Mix in a Planted Aquarium? (Tips & Tricks)

Organic potting mix and organic potting soil can be safely used in freshwater planted aquariums. They contain an abundance of beneficial nutrients to promote healthy plant growth but do not contain harmful fertilizers or pesticides that would be dangerous to fish.

Read on to learn how to choose the right potting mix and how to safely add it to your planted tank.

What potting soil can I use in my aquarium?

It’s important that you only use organic potting soil or organic potting mix in your aquarium. This is because they will not contain pesticides, herbicides, fertilizers or other inorganic materials that might harm your fish.

There are many commercial potting soil brands that are sold at most big box store gardening stores, such as Lowe’s or The Home Depot. You can also find them sold from a local nursery or boutique garden store.

Organic potting soil will be marketed as being organic and will contain the word organic on the packaging. If you are unsure if a product is organic or not then continue shopping until you find one that does.

What is the difference between potting soil and potting mix?

Potting soil and potting mix are often used interchangeably but there is a difference. Potting soil does contain some soil, along with other additives, such as peat moss, organic material and sometimes compost. Potting mix is completely sterile and does not contain any soil.

Potting mix is sometimes referred to as soilless mix or soilless medium. It’s sought after by some gardeners because there is little to no risk of it containing pathogens. It also often contains a higher percentage of mixing agents as well, such as peat moss, sphagnum moss and bark.

Both are perfectly safe for planted freshwater aquariums as long as they are organic. The organic matter and compost that’s in some potting soil is actually even more beneficial for aquatic plants.

We recommend potting soil over potting mix if you have the choice, but both will work great. We used potting mix in our latest planted tank and it turned out great:

How do you use potting soil or mix in an aquarium?

Potting soil or mix is used as a base layer in planted aquariums. We recommend adding a 1-inch layer of soil to the bare bottom of your tank, followed by a 2-inch cap of aquarium sand.

This sand cap will lock in the soil or mix and prevent it from leaching into the water column. A newly setup tank with potting soil or mix will create some bubbles and slightly disturb the capping substrate. But it will settle down over a few weeks.

It’s best to soak your soil in dechlorinated water for a few hours before putting it into the aquarium. This will allow excess gas to bubble out and will allow you to have a much better experience.

What are the benefits of using potting soil or mix in a planted tank?

Potting mix and soil contain many beneficial macro and micronutrients that plants will absorb into their roots. The result is a successful planted aquarium with beautiful, lush and healthy plants, even without added CO₂.

When should you use potting mix or soil in an aquarium?

Organic potting mix or soil can be used in both low-tech and high-tech planted freshwater aquariums. These base layer substrates will provide nutrients to help plants grow more effectively. There is no point using potting mix or soil if you do not have live plants.

You can absolutely put potting mix or soil in any aquarium size. However, tanks that are 12-inches or shorter might not provide your fish with as much room as you might have hoped. This is because a 1-inch potting mix base layer must be capped with 2-inches of sand or gravel, which leaves only 9-inches of height.

This might be more than enough for your aquascape but it’s something to think about.

How much potting soil should you use in an aquarium?

A 1-inch layer of potting soil or mix is best for most tanks. Once you get above 40-gallons you might consider increasing the soil layer to 1.5 inches. In reality, enriched potting soil will contain an abundance of nutrients so not much is necessary.

How long does potting soil last in planted tanks?

Potting mix will last at least 10-12 months before you start noticing some signs of nutrient deficiency. Potting soils might last a little longer because they sometimes contain small amounts of organic soil with microbial activity and decomposed organic material.

You can extend the life of your potting mix and soil by preparing it with soil additives. These will allow your soil to last for 5-10 years in some cases.

Can you use Miracle Grow potting soil in an aquarium?

Miracle Gro Organic Choice Potting Mix is safe for planted aquariums because it contains composted bark, sphagnum peat moss and pasteurized poultry litter. All other Miracle Gro Potting Mix products contain fertilizers that are not suitable for dirted tanks.