Whether you’re new to the hobby or have been keeping fish for years, freshwater deep sand beds might be new to you. They aren’t a very well-known type of filter.
But they can be FANTASTIC at keeping your water clean, with minimal work on your part. It’s a very natural style of fishkeeping.
Benefits of a FDSB
Why have an FDSB filter, anyway?
There are many little-known benefits to having a deep sand bed in your freshwater tank:
What does it take to have one?
Surprisingly, it’s not that hard to set up or maintain!
What You Will Need:
You can skip the highly recommended list, but your filter will work better with them! Note that some fish see scuds and blackworms as food sources, which will need to be replenished if so.
How to Set up a Deep Sand Bed Freshwater Filter
1. Add a 3″ layer of large-grain sand to your empty tank
The kind of sand you choose can make or break the success of your deep sand bed. Course, uniform grains of sand allow the mulm to penetrate through the bed to the very bottom, where it can be delivered to plant roots and processed by bacteria.
A small grain size (finer sand) will compact more. This greatly impedes the function of your filter and can result in poor plant growth and a greater danger of toxins forming below.
But too big and you won’t get those areas that allow denitrification to happen at the bottom due to having too much water diffusion.
What’s the best kind, exactly? A relatively uniform grain size of approximately .5mm is ideal, as it is designed to allow the best water flow.
CaribSea’s Crystal River sand fits the bill.
(Plus, it looks beautiful!)
Larger sand grain sizes between 1-2mm can work also, but a deeper sand bed of 4.5-5″ may be necessary in order to supply anaerobic areas.
Our Favorite Aquarium Sand:
One great option for this would be CaribSea’s Peace River.
It’s in between a gravel and a fine sand, which is PERFECT for letting oxygen and nutrients penetrate correctly and optimal biological function.
Tip: Stir in 1/2 cup of soil per 20 pounds of sand (below the top 1″ of sand) for a boost in plant growth and beneficial bacteria.
Now, you WANT the mulm to get down in the sand.
(That’s the whole point.)
The mulm is what nourishes the plants and small aquatic life.
2. Cycle the tank normally (if desired)
You CAN skip the cycling process if you add your livestock gradually and perform a “fish-in” cycle while monitoring the water quality closely.
But if you want to cycle the tank using liquid ammonia, now is the time. Adding the livestock gradually allows your filter time to adjust so it won’t get overloaded.
However, you may not want to wait. The plants do act as a water purifier, but unless they have the time they need to grow in they might not help much.
Some people like to inoculate their DSB with sand from an established tank by adding it on top of the new sand. If you can do that, it will speed things up.
3. Plant your rooting plants
Rooting plants are essential for a deep sand bed filter to work properly. Without them, your filter can become a stinky, toxic mess of hydrogen sulfide. Yikes!
Plant roots penetrate deep into the bed, helping to bring oxygen to the anoxic areas where hydrogen sulfide may build up. They keep the sand from compacting.
I recommend planting approximately 50% of the tank.
There are many great rooting plants. Amazon swords are one fantastic example of this, as they develop extensive root systems throughout the entire tank.
Be sure to choose species that are compatible with your water and fish’s pH needs.
4. Install your filter or pump
First, fill your aquarium with dechlorinated water. Then add your filter or pump. A filter or pump is important for maintaining good oxygen levels in the water.
They are also useful for removing suspended particles in the water (if using mechanical filtration).
In this setup, your filter isn’t really there to grow bacteria (unless you want it to). It’s important to keep the water just gently moving at the surface. You don’t want any splashing or bubbles driving off valuable carbon dioxide.
Also, your pump or filter should be rated for half the volume of your aquarium or less. More than that is not necessary. It does not need to be powerful.
5. Add your little critters
It’s time to add your burrowers!
These guys will churn through your sand and make your filter function properly while helping to nourish the plants.
The Malaysian trumpet snails, blackworms, and scuds should have at least 1 night to settle in (so the fish won’t bother them.)
Malaysian Trumpet Snails
These do not dig down very deep into the substrate, so they aren’t sufficient to make your sand bed work in and of themselves, but they DO help to process mulm at the top layer and add more oxygen into your DSB.
This makes your DSB work better, so they play a very useful role.
Use 2 tablespoons of Malaysian trumpet snails per 10 gallons.
Why use them?
They make a fantastic burrower in your deep sand bed, going deep down to the bottom into the oxygen-deprived areas and delivering nutrients to plants.
They also make a nutritious food source for your fish, who enjoy hunting for them. You can even culture them separately in another tank or hang them on a breeding box, so you never run out!
That said, California Blackworms can be hard to find locally. Some specialty fish stores carry them occasionally, and they often get snatched up quickly.
But check with them, and you might get lucky if you can time your visit. You can also order them online.
Use 1 tablespoon of blackworms per 10 gallons.
These little creatures aren’t a must but offer greater biodiversity to your filter and can help assist in breaking down waste.
They scramble around looking for food and produce nutritious plant fertilizer. They are also a great snack for many fish.
(Culture separately if replenishing is required.)
Snails have so many benefits and really should be kept in every tank, in my humble opinion.
Not only are they beautiful and fun to watch, but they also help process the waste and debris on top of the sand, so it sinks down easier.
They also eat algae on plants and glass. These aren’t borrowers, though; other creatures will do that job.
Add these at any point.
Some shrimp, like the Amano shrimp, are fantastic algae eaters.
They help keep the leaves of your plants healthier and your tank cleaner.
Adding the shrimp when you add the burrowers is a good idea to give them time to settle in and find some hides.
Freshwater clams are excellent for clearing up cloudy water and love to burrow (helping diffuse nutrients).
They really are no harder to keep than snails.
6. Add your fish
The time has come to add your fish! Done right, a deep sand bed freshwater filter can support a surprising number of fish.
Stock the tank and monitor the water quality closely for the first few weeks.
It’s also a good idea to add the fish gradually so you don’t overload the fragile new filter.
As long as the water is flowing through it to the main tank, it’s doing its job.
The advantage of having a detached deep sand bed filter is that the small creatures such as blackworms, scuds, shrimp, etc. are all protected from predators.
That said, it’s important that your detached filter be large enough to accommodate the filtration needs of your tank size.
When you have it in your main tank, it obviously has the most space possible.
Learning new methods for fishkeeping is always so exciting. So what about you? Did you learn something today? Or maybe you have experience keeping an FDSB and want to share your experience?