Airlift Filter: Safety and Selection for Shrimp and Fry

Ensuring safe and effective filtration in aquariums housing delicate inhabitants – shrimp or newly hatched fry – is one of the key tasks of a professional aquarist. Standard internal and external filters, based on powerful rotors and pumps, pose a serious threat to small fauna. In such specialized conditions, the airlift filter (or sponge filter) becomes the optimal, and often the only correct, choice.

1. Airlift Filter for Shrimp and Fry: A Safe Solution for Your Aquarium

The airlift filter, powered by an air compressor, has long established itself as standard equipment in breeding tanks, quarantine containers, and shrimp tanks. Its popularity is due to not only its low cost and simple design but also its unique ability to provide effective biological and mechanical filtration without the risk of injuring the smallest inhabitants.

Unlike powerful pumps, an airlift uses physics to move water, making the water intake process incredibly slow and gentle.

• For shrimp: the filter sponge serves not only as a filtering element but also as an ideal surface for the growth of biofilm – the main food source for young shrimp, such as cherry shrimp (Neocaridina davidi) or crystal shrimp (Caridina cantonensis).
• For fry: the absence of rotating parts ensures that even the smallest and weakest fry, such as apistogrammas (Apistogramma) or neons (Paracheirodon innesi), will not be sucked in.

2. How an Airlift Filter Works: How Does It Function?

The principle of operation of an airlift filter is based on the laws of hydrostatics and changes in medium density. It is a brilliantly simple solution requiring only three components: a compressor, an air hose, and the filter itself with a lift tube.

Process Mechanics:

1. The compressor supplies air through the hose to the lower part of the filter’s lift tube.
2. As the air rises, it forms air bubbles.
3. The mixture of water and air in the tube becomes significantly lighter than the clean water in the aquarium (density decreases).
4. Due to the difference in density and pressure, water from the aquarium is pushed into the lift tube, passing through the sponge.
5. The water, purified by the sponge, is expelled back into the aquarium, and the bubbles burst on the surface, further oxygenating the water.

Thus, the airlift performs two main functions simultaneously: filtration (mechanical and biological) and aeration.

3. Why is an Airlift Filter Safe for Shrimp and Fry?

The key feature that makes airlifts indispensable in sensitive aquariums is their design, which eliminates rapid currents and sharp mechanical elements.

Gentle Water Intake

Unlike standard filters where water is sucked through a narrow slit under high pressure, an airlift draws water through the vast surface area of the sponge. This ensures an extremely low suction speed, which is evenly distributed across the entire surface of the filtering material.

• Injury Prevention: The absence of turbulence and strong suction prevents tiny organisms, such as juvenile shrimp or fry of live-bearing fish (e.g., Poecilia sphenops), from entering the filter chamber.
• Biological Stability: The sponge, due to its porous structure, is quickly colonized by nitrifying bacteria (Nitrosomonas and Nitrobacter), providing highly effective biological filtration, which is critical for the health of fry.

Biofilm as Food

Sponge filters serve as an ideal substrate for the development of microorganisms and algae, which form biofilm. For shrimp, especially dwarf species, and for many types of fry in the early stages of development, this biofilm is a primary food source before they can transition to artificial foods.

4. Choosing an Airlift Filter: What to Look For?

Although the design of airlifts is simple, their selection should be thoughtful, especially considering the aquarium’s size and the type of its inhabitants.

Selection Criteria

1. Size and Volume of the Sponge (Filtering Element):

• The larger the sponge, the greater the surface area for bacterial colonization and the gentler the water intake. For a shrimp tank of 30-50 liters, it is recommended to use filters with a double sponge or large-area corner filters.

2. Sponge Density (Porosity):

• For fry and newborn shrimp, a sponge with fine pores (fine-pored) is necessary. A standard coarse-pored sponge may not handle fine suspended matter and may also allow very small organisms to penetrate.
• Expert Tip: Many professionals use sponges with PPI 30-40 (pores per inch) for maximum safety.

3. Type of Construction:

• Sponge on a Suction Cup: The simplest and most common type. Ideal for small breeding tanks.
• Double Sponge Filter: Provides double the filtration area and allows for cleaning sponges alternately without completely destroying the biological balance.
• Corner or Box Filter: Uses a sponge in a housing, sometimes with the option to add additional media (e.g., zeolite or ceramic) to enhance chemical or biological purification.

4. Compressor Selection:

• The compressor’s power should match the aquarium’s volume. It’s important not to overdo it: too strong an airflow creates excessive turbulence that can disturb fry.
• Pay attention to the noise level. High-quality diaphragm compressors, such as Eheim or Tetra, operate significantly quieter.

5. Installing and Starting Up an Airlift Filter: Step-by-Step Instructions

Installing an airlift is an intuitive process but requires following a few important steps to ensure maximum efficiency and safety.

Installation Steps:

1. Assembly: Ensure the lift tube is securely attached to the sponge and the air connector is firmly connected.
2. Placement: The filter is placed on the aquarium bottom. In breeding tanks, it is often placed in a corner or against the back wall to avoid creating strong water movement in the center.
3. Compressor Connection: Connect the air hose to the filter and the compressor. Important: Always use a check valve. If the compressor suddenly turns off (e.g., during a power outage), the check valve will prevent aquarium water from flowing back through the hose and flooding the compressor.
4. Flow Adjustment: If the compressor has a regulator or if you use a control valve on the hose, adjust the airflow. For fry and shrimp, the flow should be moderate – enough to ensure stable water lift, but without creating strong currents.
5. Startup: Turn on the compressor. In the first few hours, the airlift will primarily perform mechanical cleaning. Full biological filtration will begin 2–4 weeks after the sponge is colonized by bacteria.

6. Airlift Filter Maintenance: Cleaning and Replacing Filter Media

Airlift filter maintenance is crucial for maintaining the biological safety of the aquarium. The main rule: never clean the sponge under running tap water!

Sponge Maintenance Rules

1. Cleaning Frequency:

• Since airlifts are typically used in aquariums with low bio-load (fry, small numbers of shrimp), cleaning is not required often – once every 2–4 weeks or when the water flow noticeably decreases.

2. Cleaning Process:

• Turn off the compressor.
• Carefully remove the filter from the aquarium.
• Place the sponge in a container with siphoned aquarium water (water that you typically remove during a water change).
• Gently squeeze the sponge several times to remove large debris and silt. The goal is not to sterilize but merely to remove excess mechanical impurities.

3. Sponge Replacement:

Sponge replacement is rarely needed – only if the material begins to degrade or lose its shape (usually after several years of use). When replacing, it is recommended to first use the new sponge together with the old one for a week so that the new one can become populated with beneficial bacteria.

7. Airlift Filter: Answers to Frequently Asked Questions (FAQ)

Question: How effective is airlift filtration?

Answer: An airlift provides excellent biological filtration due to the large surface area of the sponge. Mechanical filtration is moderate but sufficient to maintain cleanliness in aquariums with low stocking densities (breeding tanks, shrimp tanks).

Question: Can an airlift filter be used in a large aquarium?

Answer: For aquariums over 100 liters, an airlift is rarely used as the sole filter, especially if large fish are kept (e.g., angelfish Pterophyllum scalare). However, it can serve as an excellent additional biological filter, maintaining stable water parameters.

Question: Does an airlift filter create noise?

Answer: The noise comes not from the filter itself but from the compressor and from the bubbles bursting on the water surface. Using a high-quality, insulated compressor and placing it away from the aquarium (e.g., in a cabinet) significantly reduces noise levels. Using a spray bar at the outlet of the lift tube also helps.

Question: Does an airlift filter replace chemical filtration?

Answer: No. An airlift in its classic form (sponge) provides mechanical and biological filtration. To remove chemical impurities, odors, or medications, specialized box filters that can accommodate activated carbon or other chemical media will be required.

8. Interesting Facts About Airlift Filters and Their Applications

Airlift systems are not just a sponge and a tube; they are a technology that has found wide application not only in hobbyist but also in industrial aquariums.

• History: Airlift systems were among the first mechanized filters used in aquariums in the early 20th century, before the advent of modern submersible pumps.
• Quarantine and Treatment: Airlifts are ideal for quarantine aquariums, as their sponges are easy to sterilize (or replace) after treating fish. Furthermore, the gentle flow does not stress sick individuals.
• DIY Solutions: Due to their simplicity, airlift filters are among the most popular objects for DIY construction. Aquarists often create powerful systems using large plastic containers and foam mattresses for maximum filtration area.
• Multifunctionality: The airlift principle is used not only in filters. It is the basis for the operation of some protein skimmers (floaters) in marine aquariums and in water circulation systems in industrial fish farms.

Thus, the airlift filter is a reliable, economical, and, most importantly, safe tool for anyone involved in fish breeding or keeping delicate invertebrates. Its effectiveness in biological purification and gentle handling of water make it an indispensable element in the arsenal of an experienced aquarist.