Hey, got a pond or aquarium? Cool! You’re probably interested in aquatic compost!
Aquatic compost is a type of soil that is safe for fish, and is made specifically to keep plants anchored at the bottom of ponds or aquariums.
In the article, we’ll teach you everything you need to know about aquatic compost: what it is, how to use it, if it’s fish safe, and what you can use as an alternative.
What is Aquatic Compost
Despite its name, organic compost has very little to do with decaying organic matter. Aquatic compost is a specially made soil specifically designed to anchor plants to the pond or aquariums bottom.
It functions the same way as garden soil; it gives plants stability and a nutrient base, except it is specific to plants that will be grown underwater.
How Is Aquatic Compost Different Than Garden Soil
Aquatic compost differs from garden soil in two main ways.
- Aquatic compost is heavier than garden soil. It has to be heavy, otherwise the compost would float in the pond or aquarium instead of sink, and just create a big, murky, brown mass when mixed with the water.
- The fertilizer is an extremely slow-release fertilizer. This way it releases nutrients slowly, so it doesn’t harm fish, and will not affect the pH.
Is Aquatic Compost Safe For Fish?
Yes, aquatic compost is safe for fish. By adding aquatic compost to your fish tank or pond, you are giving your fish a more natural habitat. They aren’t used to living in a place with a glass or tarp floor!
Now the bigger question is why wouldn’t regular soil be safe for fish?
Regular garden soil is not safe for fish because it contains nutrients that can harm fish. The soil also introduces pH change to the water, which could create a challenge for the fish to survive.
Aquatic compost is made for aquatic ecosystems, so it’s safe for fish and aquatic creatures. It has no harmful nutrients and a neutral pH which makes it great for fish tanks and ponds.
Can I use Aquatic Compost as a Substrate?
Sure, you can use aquatic compost, we call it a substrate because it’s a gardening substrate. Garden substrates are stuff used as the base layer for a garden.
You’ll see things called gardening substrates and they are usually soils but could also include sand, compost, and so on.
Now if you’re thinking about planting with aquatic compost, say in a regular garden or potted plants, the answer is yes, you can but you probably shouldn’t.
Aquatic compost is full of clay which is heavy and dense soil. One of the problems with growing anything in clay soil is that water doesn’t drain well, which can be a problem.
The properties of clay can also clog gutters and sewer drains, which can damage the infrastructure after it rains. Clay soil can inhibit plant roots from reaching into the soil, so the plant cannot access nutrients or properly use the water.
Clay soils can have nutrient deficient soil, or have nutrient deficiencies, so every time you put fertilizer down it becomes nothing more than wasted money without the surrounding environment having enough microorganisms to break the nutrients down a bit.
Most plants want well-draining soil, rich in organic matter, while there can be shrub/tree species that can “handle” or tolerate, “heavy” or poorly draining soils, because they are able to shed excessive moisture better than other plants.
For these species, adding organic matter in clay soil will improve the drainage and make more nutrients available.
If you have a plant that doesn’t tolerate wet soils, I would avoid clayey areas or amend the soil with compost beforehand.
That will give your plant the best chance of success and lessen the chance you will have to replant because of poor growing conditions.
Is Aquatic Compost Acidic?
Aquatic compost is totally neutral, no acidity at all, which really shouldn’t surprise you if you’re thinking about what would make it neutral.
Garden soils are acidic to alkaline – there are some acidic soils, and some that are downright alkaline (and different garden beds and soils in your own backyard might have different acidity).
In an aquatic ecosystem, there still has to be a balance for everything living inside the ecosystem over just adding nutrients for the plants.
When you plant in water, everything shares the same space – plants, water, fish, microorganisms.
The aquatic compost’s acidity has to rise or fall, and that would not only affect the plants but the water quality, and also the fish’s livelihood.
How Much Does Aquatic Compost Cost?
Aquatic compost isn’t consistent in price. You can buy a 10lbs bag for $10 all the way up to $40 bucks.
If you were to place aquatic compost in a 5-gallon aquarium with the appropriate depth (2 inch layer of the substrate to allow roots to anchor to the bottom), you would need at least 10lbs to do that.
One 10lbs bag of compost can be enough to do about three 5-gallon aquariums.
If you’re putting down substrate for something like a lot more area to cover like a pond, it’s going to be much more expensive because a much larger area will be lots of layers.
Aquatic Compost Alternatives
If you don’t like the look of aquatic compost, or maybe you just don’t like the look of it, there are other options you can use.
Gravel
Gravel is a sort of rock, used in a variety of applications like landscaping, construction, and way cheaper than sand in aquariums.
Gravel is a great option for aquariums, because it is hard, resistant, easy to clean, and relatively cheap compared to other substrate material.
Gravel will support plant roots without contaminating acidity, nutrient level, or the quality of the water.
You want to choose the correct gravel size, for example 2-3mm is a good size for plant growth. If it is too course, the roots of plants may not establish.
Kitty Litter
There’s all kinds of kitty litter material (not just clay), but clay is the most common. As all cat owners know, it’s utilized to absorb their liquid waste, but kitty litter can also be used as a substrate for aquatic plants.
When kitty litter gets wet, it will clump together. This, in addition to anchoring plant roots really well, also allows kitty litter to keep any excess kitty litter from floating to the surface.
Always test before adding to an aquarium or pond! Not all kitty litter is safe for live plants!
Horticultural Grit
Horticultural grit is a thing gardeners commonly use to give the plant the stability it needs, help keep the roots steady, and as a deterrent from bugs.
Horticultural grit is made up of many kinds of materials, but typically consists of sand, ground limestone, or oyster shell powder. Horticultural grit can be found online and at many nurseries and garden centers.
DIY Aquatic Compost
You can also create your own aquatic compost using soil in your backyard. This is by far the simplest and least expensive method to add a layer of substrate to an aquarium or pond.
While soil is still relatively light, which is why DIY aquatic compost will still require a thin layer of gravel or sand to hold the soil down, this option will still be less expensive than using just gravel or just sand as what is underneath the aquatic plants.
How to Make Aquatic Compost
If you need a lot of aquatic compost and you’re planning to buy it in bulk it can cost a lot. If you don’t want to buy aquatic compost, you can easily make it yourself using a few simple steps.
First, you will need to gather your equipment. You will need:
- A shovel
- A bucket
- A sieve or sifter
- A baking tray (or 2)
- Gravel or sand
Step 1
Using your shovel, dig some dirt from your garden or lawn.
Best bet is to find a cheap bag of dirt, with no peat and organic too!
Step 2
Sift the soil for rocks, sticks, bugs and debris. You’ll need to sift enough soil to have a two-inch layer down in your aquarium/pond.
In a 5-gallon tank, you’d need to sift about 4-liters of soil to create a two-inch layer.
Step 3
You’re gonna take that sifted soil, and put some on a baking sheet in a thin layer. Bake the soil at 20 degrees Fahrenheit for 30 minutes.
Baking the soil will kill any bacteria or microorganisms that is not going to be wanted in the aquarium or pond.
Step 4
Once you’ve baked and cooled your soil, spread it across the bottom of an empty aquarium or pond, and level the soil.
Now, is when you can add your plants to the soil.
Step 5
Since this is still just soil, it will be substantially lighter than a real aquatic compost.
To prevent the soil from floating or mixing in the water, add a thin layer of gravel or sand on your soil as a layer. You can place it carefully around the stems of plants so it doesn’t harm them. This will give them a little more support.
Step 6
This might be the hardest step! You’re ready to add water, but adding it too quickly will agitate the soil.
Agitating the soil might mix it up with the water, if the soil gets mixed in with the water then parts of it will float at the surface of the water, and some parts will settle at the top of your layer of gravel or sand.
So the best method of adding water to an aquarium or pond is to pour the water in carefully along the side, until it is full.
Final Thoughts
Aquatic soil is a special substrate that possesses a very neutral acidity, slow-releasing fertilizers, and weighs and is denser than your average gardening substrate.
It is safe for plants, fish and microorganisms, making it safe for all living things in your water ecosystem to success.
There are other alternatives to aquatic soil that can be used in planted tanks or ponds, such as gravel, and horticultural grit, there is a viable option for everyone.