Deltec Nitrate Reactor

A Deltec nitrate reactor removes nitrates from your aquarium water by running tank water through a chamber packed with biological media and a controlled carbon source, allowing anaerobic bacteria to convert nitrates into harmless nitrogen gas. If you're dealing with persistent nitrate creep in a reef tank or heavily stocked fish-only system, this is one of the most hands-off long-term solutions available.

Deltec is a German manufacturer that has been making high-end aquarium equipment since the 1980s. Their nitrate reactors are built to commercial-grade standards, use quality acrylic chambers, and are engineered for consistently low nitrate output with minimal fuss once dialed in. This guide covers how Deltec reactors work, which models exist, how to set one up, and what results you can realistically expect.

How a Deltec Nitrate Reactor Actually Works

Nitrate reactors operate on the principle of anaerobic denitrification. Regular biological filtration (the nitrogen cycle) converts ammonia to nitrite to nitrate, but it stops there because that final step requires an oxygen-depleted environment. A nitrate reactor creates exactly that environment inside a sealed chamber.

Water passes through the reactor body very slowly, spending enough time inside that dissolved oxygen drops to near zero. Anaerobic bacteria in that zone then process nitrates all the way to nitrogen gas, which off-gasses harmlessly. The bacteria need a carbon food source to do this work, and that's typically ethanol (vodka dosing), sugar solutions, or purpose-made carbon sources like Deltec's own Carbon Source.

The Anaerobic Chamber Design

Deltec reactors use a recirculation pump to keep water moving inside the chamber at a controlled rate, separate from the main flow rate coming in from your sump or tank. This internal recirculation is important: it distributes the carbon source evenly through the media bed and prevents dead spots where hydrogen sulfide can accumulate (which would be toxic if it escaped into your main tank).

The outlet water from the reactor exits with very low oxygen and potentially some hydrogen sulfide. Deltec builds a secondary chamber or recommends directing outlet water into a sump with strong aeration before it mixes with tank water. This is not optional. You cannot run reactor effluent directly into your display tank without aeration first.

Media Choices

Deltec reactors work with several media types: - Sulphur media: Slow-release, self-sustaining, but lowers pH slightly and works best for lower-flow applications - Bioethanol carbon source with inert ceramic media: The approach Deltec primarily recommends for their modern reactors - Seachem Matrix or similar porous rock: Used by some hobbyists as the bacterial substrate with liquid carbon dosing

For most users, the combination of inert ceramic rings and a liquid carbon source like Deltec Carbon Source or plain ethanol gives the most predictable control.

The Deltec NR Product Line

Deltec offers several reactor sizes designed for different system volumes:

NR 100: Designed for systems up to about 250 liters. This is the entry point into Deltec reactors, suitable for a typical 60-75 gallon reef with a moderate bioload.

NR 200: Steps up capacity for systems in the 250-600 liter range. This covers most hobbyist reef tanks in the 100-150 gallon class.

NR 509: A serious unit for systems from 500 liters to well over 1,000 liters. You'll see these on large mixed reef tanks and fish-heavy systems where other nitrate control methods haven't kept pace.

NR 5000 series: Professional-grade units for public aquariums, commercial operations, and very large private systems. These are not typical home aquarium purchases.

Each unit includes the reactor body, feed pump fittings, and basic instructions. You need to supply a separate feed pump (usually a small peristaltic pump or a controllable powerhead with a flow restrictor), a carbon source, and appropriate plumbing to route effluent through aeration before return.

Setting Up a Deltec Nitrate Reactor

Setup takes a few hours and involves four main steps: plumbing, priming, setting flow rate, and dialing in carbon dosing.

Plumbing and Placement

Mount the reactor in your sump or equipment cabinet where effluent can drain by gravity into a chamber with a skimmer or strong surface agitation. The feed line typically comes from your return pump output, stepped down through a ball valve to a very low flow rate, often 10-30 liters per hour depending on reactor size.

Connect the internal recirculation pump. On Deltec units this is usually a small magnetic-drive pump rated around 100-200 liters per hour that keeps water circulating internally regardless of the main feed flow.

Setting the Flow Rate and Carbon Dosing

This is where most people struggle. The goal is to match your carbon dosing rate to your bioload-driven nitrate production. Start conservatively: set the feed flow to the minimum recommended for your reactor size and begin carbon dosing at roughly half the maximum rate.

Test your nitrates every 2-3 days during the first two weeks. If nitrates drop too fast (below 5 ppm in a reef tank), reduce carbon dosing. If they're not dropping, increase slightly. A 10-20% adjustment per week is enough; chasing it with large swings causes instability in the bacterial colony.

Target ranges for most tanks: 5-15 ppm for mixed reefs, below 5 ppm if you're keeping sensitive SPS corals.

Monitoring the Effluent

Buy a basic ORP (oxidation-reduction potential) meter or probe. Effluent from a properly running reactor reads negative ORP, sometimes below -100mV. If it reads positive ORP, the bacteria aren't in full anaerobic mode and the reactor isn't denitrifying effectively. If it's extremely negative (below -300mV) and smells of sulfur, you're in hydrogen sulfide territory and need to reduce carbon dosing and increase aeration.

Deltec Reactor vs. Alternative Nitrate Control Methods

It's worth being honest about where nitrate reactors fit relative to other options.

Refugium with macroalgae (Chaeto): Easier, adds oxygen to the system, no hydrogen sulfide risk. A refugium can realistically handle a lightly to moderately stocked reef tank. The limitation is export: you have to harvest the algae regularly, and it doesn't scale as efficiently for heavy fish loads.

Biopellets: Easier to maintain than a nitrate reactor, use similar anaerobic bacterial principles, but work aerobically. Biopellets are a good middle ground. The downside is they require consistent flow and can cause bacterial blooms if overdosed.

Vodka/ethanol dosing directly: This is essentially what a nitrate reactor does, but you're doing it manually without the contained environment. More risk of overdose without the buffering effect of the contained reactor.

Water changes: Always valid, always safe. For a heavily stocked system producing 5-10 ppm nitrate per day, large frequent water changes become expensive and time-consuming.

A Deltec reactor makes the most sense when you have a large system, high bioload, and want to reduce your water change frequency without constant manual intervention. For smaller reef tanks under 100 gallons with light fish loads, a refugium or biopellet reactor is often simpler and cheaper.

You can find comparisons of the best approaches in our guide to Best Aquarium Equipment if you want to evaluate multiple filtration methods side by side.

Maintenance and Common Problems

Once running, Deltec reactors need relatively little attention.

Monthly: Check the feed flow rate hasn't drifted. Ball valves and needle valves can shift slightly over time, especially if there's any calcium precipitation.

Every 3-6 months: Clean the internal recirculation pump. Biofilm buildup reduces flow and can cause inconsistent internal circulation.

Annually or as needed: Replace media. Ceramic media lasts indefinitely. Sulphur media gradually depletes and should be topped up or replaced when flow restriction increases noticeably.

Problem: reactor effluent smells like rotten eggs. This means hydrogen sulfide is forming. Reduce carbon dosing by 30%, increase feed flow slightly, and ensure the effluent aerates thoroughly before entering the display system. Check that your aeration chamber has enough turbulence.

Problem: nitrates not dropping. The bacterial colony may not be established yet (this typically takes 4-6 weeks). Also check that the recirculation pump is working and that your carbon dosing is actually entering the reactor rather than flowing through too fast.

Problem: nitrates crashing to zero. You've overdosed carbon. Reduce immediately. Chronically near-zero nitrates in a reef tank can cause zooxanthellae loss in some corals.

For a full look at top-tier equipment options at various price points, see our Top Aquarium Equipment guide.

FAQ

How long does it take a Deltec nitrate reactor to work? Expect 4-6 weeks before the bacterial colony is fully established and nitrates begin dropping consistently. Some tanks see results in 2-3 weeks. The patience-test period is real, but don't chase it by dumping in extra carbon. Slow and steady establishment produces a more stable colony.

Can I use a Deltec nitrate reactor on a freshwater tank? Yes. The denitrification biology is the same. The setup is identical. If you're running a heavily stocked cichlid or discus tank where nitrates climb fast, a reactor works well. The one difference is that freshwater tanks often tolerate higher nitrates than marine, so you might not need one unless you're keeping very sensitive species.

What carbon source does Deltec recommend? Deltec sells their own Carbon Source product, which is an ethanol-based solution formulated for use in their reactors. Plain food-grade ethanol (clear vodka works fine) is a well-accepted alternative. The concentration matters more than the source: start at the minimum dosing rate and adjust based on test results. Avoid sugar-based carbon sources in reactors because they're harder to dose precisely and can promote bacterial blooms.

Do Deltec reactors need a dedicated controller? No, but a controllable peristaltic pump for the feed line makes fine adjustments much easier. Peristaltic pumps, like the ones from Kamoer or Jebao, can be set to exact milliliters per hour, which takes the guesswork out of flow calibration. A standard ball valve works but requires more frequent checking and adjustment.

Conclusion

A Deltec nitrate reactor is a legitimate long-term solution for nitrate management in larger, heavily stocked aquariums. The NR series is well-engineered, uses quality components, and when set up correctly produces stable low nitrate levels with minimal maintenance compared to daily carbon dosing or heavy water change schedules. The learning curve is in the first six weeks of calibration. Get your flow rates and carbon dosing dialed in during that period, and the reactor essentially runs itself with monthly check-ins. If your nitrates are chronically above 20 ppm despite regular water changes, this is worth serious consideration.