Eheim Clear Tank 300

The Eheim Clear Tank 300 is an ultraviolet clarifier designed to clear green water from freshwater aquariums up to 300 liters (about 79 gallons). It uses a UV-C lamp to kill the suspended algae cells responsible for turning your water pea soup green, and it works quickly, often clearing a tank in 3 to 7 days of continuous operation. If green water is your problem, the Eheim Clear 300 is a reliable, low-maintenance solution from a brand with decades of aquarium equipment history.

This article covers how the Clear 300 works, how to set it up, what maintenance it requires, and how it compares to other UV clarifiers in the same size range. You'll also find answers to the most common questions people have after buying one.

How UV Clarification Works

Before getting into the Clear 300 specifically, understanding the mechanism helps you use it correctly.

Green water is caused by free-floating single-celled algae, Euglena and Chlorella being the most common. These cells are too small to be caught by standard mechanical filtration. They pass right through filter sponges and filter floss. What kills them is ultraviolet light in the 254-nanometer wavelength range, which disrupts their DNA and prevents reproduction.

The Eheim Clear 300 runs tank water past a UV-C lamp inside a sealed chamber. The exposure time is calibrated to kill algae at the rated flow rate. Water flows in, passes the lamp, and exits clear. Dead algae cells clump together and become large enough for your filter to remove.

What UV Does Not Do

UV clarification kills free-floating organisms in the water column. It does not kill algae growing on glass, rocks, or substrate. It also does not eliminate the nutrients (nitrate, phosphate) that fed the algae bloom in the first place. If you clear a green water outbreak with the Clear 300 and don't address the underlying cause, the bloom will return when you switch the unit off.

Eheim Clear 300 Specs and Features

The Clear 300 handles tanks up to 300 liters (79 gallons) and runs on a 9-watt UV-C lamp. Flow rate is up to 750 liters per hour (about 198 GPH), which the unit achieves through an integrated pump. You don't need a separate pump to run it.

The unit connects to an air pump or can run inline from a filter outlet depending on the configuration. The housing is compact at about 350mm long, making it easy to place in a sump or hang on the back of the tank.

Integrated Pump vs. External Filter Connection

The Clear 300 includes an integrated pump motor. This means you can run it as a standalone unit with its own circulation, independent of your main filter. The connection to your air pump approach is a common point of confusion in reviews. The Clear 300 does not use an air pump. It has an electric pump motor in the head unit.

You can also connect it in-line with an external canister filter like the Eheim Classic 250 or Eheim Professionel 4 if you want the UV integrated into your main filtration circuit. For most setups, running it standalone is simpler and equally effective.

Setting Up the Eheim Clear 300

Setup takes about 20 minutes and requires no special tools.

Step 1: Prime the Unit

Submerge the intake and outlet tubes and let the chamber fill with water before plugging in. Running the pump dry even briefly can damage the impeller. Open the air release valve at the top of the UV chamber while filling to purge any trapped air.

Step 2: Position the Intake and Outlet

Position the intake in the area with the worst algae concentration, typically the middle of the water column. Point the outlet toward the surface to maximize circulation. Keep the intake at least 4 inches from the outlet to prevent short-circuiting (water taking the shortest path from intake back to outlet without passing through the UV chamber).

Step 3: Plug In and Check Flow

With everything submerged and air purged, plug in the unit and verify flow from the outlet. Weak flow usually means trapped air in the chamber. Open the air release valve again briefly while the pump is running to clear it.

The UV lamp indicator light on the head unit confirms the lamp is operating. The light is blue and visible through the housing when the lamp is on.

For protein skimmer recommendations and other filtration gear that pairs well with UV clarifiers, the best protein skimmer for 300 gallon tank guide covers options at multiple price points, though note the Clear 300 itself is designed for much smaller systems.

Maintenance Schedule

The Eheim Clear 300 needs two types of regular maintenance: quartz sleeve cleaning and lamp replacement.

Quartz Sleeve Cleaning

The UV lamp sits inside a quartz glass sleeve that protects it from the water. Mineral deposits and biofilm build up on the sleeve over time, reducing UV transmission and effectiveness. Clean the sleeve every 3 months by removing it and wiping it down with a cloth dampened with white vinegar. Eheim sells a cleaning cloth specifically for this purpose but any non-abrasive cloth works.

A dirty quartz sleeve is the most common reason people report their Clear 300 stopping working. The lamp may be fine; the sleeve is just blocking the light.

Lamp Replacement

The UV-C lamp degrades over time even if it still lights up. Eheim recommends replacing the 9-watt lamp every 6,000 hours of operation, roughly once per year at 16 hours daily use. Eheim sells replacement lamps (part number 4011708370209) for around $15 to $20. Generic 9-watt T5 UV-C lamps from other manufacturers also fit but quality varies.

After replacing the lamp, reset any hour counters you're tracking and note the replacement date on the unit with a piece of tape.

How Long Until Green Water Clears?

With the Clear 300 running continuously on a properly sized tank, green water usually starts visibly clearing within 2 to 3 days and is fully clear within 5 to 7 days. Some people see faster results on smaller tanks or lighter blooms.

Factors that slow results include: - Running the unit on a tank larger than 300 liters - A partially blocked quartz sleeve - An old lamp past its service life - Exceptional nutrient load driving rapid algae regrowth

If you don't see improvement after 10 days, check the lamp and sleeve first before assuming the unit is defective.

Eheim Clear 300 vs. Other UV Clarifiers

The Clear 300 occupies the mid-range of the UV clarifier market. Here's how it compares to the main alternatives.

Eheim Clear 300 vs. Tetra GreenFree UV Sterilizer

The Tetra GreenFree is a cheaper option in the same tank size range, running around $25 compared to the Eheim's $50 to $60 price. It uses a 5-watt lamp and is less powerful. For light green water issues, the Tetra works. For persistent heavy blooms, the Eheim's higher wattage and better build quality give better results.

Eheim Clear 300 vs. Aqua Ultraviolet Advantage 8W

The Aqua UV Advantage 8W is in the same wattage class and also runs about $50. Build quality is comparable. The Aqua UV has better lamp accessibility for replacements, while the Eheim has a slightly simpler installation process. Both are solid options at this price.

For a broader look at aquarium filtration and clarity gear, the best aquarium equipment guide covers UV sterilizers and clarifiers across tank sizes.

FAQ

Does the Eheim Clear 300 work for saltwater tanks? Yes. UV clarification works the same in saltwater. The Clear 300 is rated for freshwater and marine use. It's more commonly used in freshwater because saltwater tanks typically run protein skimmers that help manage algae indirectly, but green water can occur in saltwater too and the Clear 300 handles it.

Can I run the Eheim Clear 300 continuously? Yes, continuous operation is fine and is actually recommended during a bloom treatment. Between treatments, some hobbyists switch it off to avoid reducing beneficial bacteria levels in the water column, though the impact on cycling bacteria is minimal in a well-established tank.

Will the Eheim Clear 300 hurt my fish or beneficial bacteria? The UV only affects organisms passing through the unit. Fish, snails, and shrimp are not harmed. Beneficial bacteria on filter media, substrate, and decorations are not affected because they're not free-floating. Only free-swimming microorganisms in the water column are exposed.

What's the difference between UV clarifiers and UV sterilizers? UV clarifiers are sized and rated to kill algae, which requires lower UV doses. UV sterilizers are built to eliminate pathogens like ich parasites and bacteria, which requires higher doses and slower flow rates. The Eheim Clear 300 is specifically a clarifier and is not marketed or tested as a sterilizer for disease control.

Key Takeaways

The Eheim Clear 300 is a solid, reliable UV clarifier for tanks up to 79 gallons. It's straightforward to set up, effective against green water, and requires minimal maintenance when you clean the quartz sleeve every 3 months and replace the lamp annually. The integrated pump makes it a self-contained unit that doesn't require connection to your existing filter circuit.

If green water is your problem and your tank is under 300 liters, this unit will solve it within a week. Just make sure you also address the root cause, typically excess nutrients or too much light, so the problem doesn't come back once you switch the unit off.