Aquaponics keeps gaining fans as a practical, low-fuss way to grow your own food, and it’s a hobby almost anyone can pick up. Early on in your research you’ll run into phrases like “flood and drain aquaponics” or “ebb and flow” — these describe a growbed-and-fish-tank setup where a pump sends water up to the growbed and a siphon carries it back down to the tank. It’s one of the most popular routes for home builders, so let’s break down how it actually works and whether it fits what you’re trying to build.
The basics of a flood and drain system
Building an aquaponics system means putting together the plumbing to move water from your fish tank up to the growbeds — you can also add a filter and biofilter if you like. You’ll need to fill your growbed with a growing medium too, which we’ll cover below. That media does double duty: it gives plant roots something to anchor into while they reach for the nutrient-loaded water, and it hosts the bacteria colony that’s arguably the most important part of the whole system. These bacteria turn fish waste (ammonia) into nitrates, which the plants absorb as food — and in doing so, the plants clean the water and keep it safe for your fish. Get it dialed in and the system practically runs itself.
There are two main ways to deliver water to your plants:
Flood and drain
A pump moves water from the fish tank up into the growbed, filling it until nearly all the media is submerged (you decide exactly how high). A siphon then drains that water back to the fish tank. While the siphon is draining, the pump keeps running the whole time — but water leaves faster than it’s being added, so the water level rises and then falls in a repeating cycle. Set it up once and it runs on its own from there.
Continuous flow
The other option keeps water flowing constantly without ever flooding the growbed — plant roots simply extend down into the moving water to feed. This isn’t a method I’d recommend, though, since it tends to starve the roots of oxygen.
Popular flood and drain setups
A flood and drain system works best when the growbed sits higher than the fish tank, so gravity and a siphon can do the work of draining it. Keep in mind there’s usually a short lag between the growbed flooding and the water returning, which can temporarily drop your fish tank’s water level — make sure it doesn’t drop too far. If you’re running several growbeds that pull a lot of water at once, a sump tank is worth adding. Here are the setups people build most often.
IBC totes
This is my personal favorite way to get started — it’s straightforward, and IBC totes are frequently available for free. Just make sure any used tote is thoroughly cleaned before you add water, fish, or plants. The build involves slicing off the top third of the tote (cage included), flipping that piece over, and setting it on top of the remaining base — giving you two stacked containers. A helpful trick: cut an opening in the front of the lower section so you can actually reach your fish. Fish live in the bottom container, water gets pumped to the top section, and it cascades back down through a siphon — which aerates the water along the way, potentially saving you from needing a separate air pump.
Barrelponics
This works the same way as the IBC tote method, just using a food-grade barrel of 55 gallons or more instead. Stick to a barrel that’s rated food-safe — with a barrel that previously held chemicals, you can’t be sure what may have soaked into the plastic. As with the totes, you’ll cut off and invert the top third to form your fish tank and growbed, and you may want to build a support frame depending on your setup.
Choosing grow media
Once your fish tank and growing container are connected by a pump and a short run of pipe, it’s time to fill the growbed with media. This isn’t just a stand-in for soil to hold roots in place — it’s also where the ammonia-converting bacteria live. A few common choices:
Clay pebbles (hydroton)
These lightweight pebbles are heat-treated to create a porous surface, giving bacteria more room to colonize. They’re roughly marble-sized, smooth, and easy to work with. Their combination of high porosity and small size means your growbed drains quickly, and they’re generally seen as an eco-friendly choice that makes pulling plants (roots and all) simple. They suit short flood-and-drain cycles particularly well, though that fast drainage can work against you in hot climates by drying out and wilting your plants. One quirk to watch for: the pebbles tend to float for the first few months, raising the odds they’ll get pulled into your pipes or filters.
Lava rock
Formed when volcanic lava cools too quickly for trapped air to escape, lava rock ends up naturally porous — great for giving nitrifying bacteria plenty of surface to grow on. It’s surprisingly lightweight and pH-neutral, so it won’t throw off your system’s chemistry. On the downside, it has sharp edges that can cut your hands or damage plant roots, so handle it carefully.
River rock
Naturally smoothed by flowing water, river rock comes in a range of sizes. The smallest pieces tend to work their way into filters and pipes and cause blockages, so medium-sized stones are usually the sweet spot between surface area and flow. Always rinse river rock before use, since it often carries limestone residue that can push your water’s pH up. It’s also heavy, so make sure your container and its support can handle the load.
Siphon types
A siphon is what makes draining the growbed possible — it empties the bed back into the fish or sump tank even while the pump keeps running. There are a few designs to pick from.
Bell siphon
This is the most widely used design. A tube runs up through the bottom of the growing container, stopping about an inch below the top of the media — that gap creates a dry zone that helps keep algae from forming. A second, wider cylinder surrounds this tube and extends higher than the media, keeping loose media out of the siphon mechanism. Small holes near the bottom of that outer cylinder let water in, and it rises until it reaches the top of the inner tube. Once it does, rising water pressure pushes the trapped air out of the tube, and the water rushes back down into the fish tank. As the water level drops, air pressure inside the siphon builds back up and stops the flow — simple and reliable.
U siphon
Usually cheaper to build but trickier to tune correctly. A tube rises from the base of the container to your target water height, bends into a U shape, then runs back down to the tank base — it can also terminate inside the growbed itself, as long as it has holes along its sides. As water rises in the growbed, it fills the U bend, and once it crests the top of the U it spills over and flows down toward the tank. If you want to keep a bit of standing water at the bottom of the growbed, add a floating disc to the pickup pipe — as the water rises and the float lifts, it uncovers the siphon’s entrance and lets water start flowing in.
Timer-controlled valve
A third option uses a timer to open a valve and let water drain back to the fish tank. The obvious downside is that this depends on electronics and electricity — one more component that could fail. In practice, the timer runs the pump to fill the growbed, and once it’s full, the valve opens on schedule to drain the water back through a simple pipe. Whatever the method, your pump needs to fill the bed faster than the water can drain out.
Do you need a sump tank?
A sump tank exists to keep your fish tank’s water level stable. As a rule of thumb, if your fish tank holds as much water (or more) than your growbed, you probably don’t need one. For example, a 100-gallon fish tank paired with a 100-gallon growbed typically only moves around 40 gallons per flood-and-drain cycle, since the growing media itself takes up about 60% of the growbed’s volume. But if that same 100-gallon growbed is paired with just a 50-gallon fish tank, pulling 40 gallons for each cycle would leave the fish dangerously short on water — that’s when a sump tank becomes necessary. Essentially, a sump tank just adds extra water volume to the system, with water flowing from the fish tank into the sump and then on to the growbeds.
How fast should the water cycle?
The general guideline is to cycle your fish tank’s entire water volume through the growbed once every hour — meaning the full volume passes through the growbed about 24 times over the course of a day. This keeps the ammonia-to-nitrate conversion running smoothly and gives your plants a steady, reliable supply of nutrients.
What is a split flow?
You may run across the term “split flow,” particularly in systems that include a sump tank. It just means pumping water toward more than one destination at once. If you’re using a sump tank, you might not want to send every drop to the growbeds — instead, you can split the flow so some water goes to the growbeds and some goes back to routing through an aerator, boosting the oxygen available to your fish. A split flow can also help keep the fish tank from dropping too low, or let you control how quickly the growbed fills.
There’s no shortage of ways to design and run an aquaponics system, but flood and drain remains the simplest and most beginner-friendly starting point. Once you’ve got the fundamentals down, you’ll be well positioned to experiment with other approaches if you want to.