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 a FDSB filter, anyway?
There are many little-known benefits to having a deep sand bed in your freshwater tank:
- Lower nitrates naturally
- Reduce or eliminate tedious gravel vacuuming
- Superior plant growth
- Less reliance on commercial filtration
- Can support a heavier load of fish
- Pristine water quality
- No stirring up of the sand required
- The substrate is the biological filter
- Great for fish that like to dig (including goldfish!)
What does it take to have one?
Surprisingly, it’s not that hard to set up or maintain!
What You Will Need:
These are the musts…
- Large grain course sand (I highly recommend Crystal River by CaribSea)
- Rooting plants (Swords, Cabomba, Vallisneria, etc.)
- Small power filter or submersible pump
(You technically can skip the following, but your filter may not be as powerful.)
(But beneficial 🙂 )
- Freshwater Scuds/Arthropods
- Digging fish (goldfish, loaches, etc.)
- Freshwater snails (ramshorn, melano, bladder, etc.)
- Freshwater clams
Note that some fish see scuds and blackworms as a food source and these 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 of a 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 which allow denitrification to happen at the bottom due to having to much water diffusion.
What’s the best kind, exactly?
A relatively uniform grain size of approximately .5mm is the 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.
One great option for that 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.
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.
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.
But 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.
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 for 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.
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 on breeding box so you never run out!
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.
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…
… They help process the waste and debris on top of the sand so it sinks down easier.
They also eat algae on plants and the glass.
These aren’t burrowers though – other creatures will do that job.
Add these at any point.
Some shrimp like 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.
7. 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.
Instead of having the FDSB in your main aquarium, you could also put it in other places.
… A hang-on breeding box (or hang on refugium)…
As long as water is flowing through it to the main tank, it’s doing its job.
The advantages of having a detached deep sand bed filter is firstly that the small creatures such as blackworms, scuds, shrimp etc. are all protected from predators.
Nifty, right? 😉
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 a FDSB and want to share your experience?
… Leave your comment below.
I love hearing from my readers!