Paludarium Filter and Pump Guide

What Does a Paludarium Pump Need to Do?

A paludarium pump may need to move water from a shallow aquatic basin to an elevated return, drip wall, stream, or waterfall. That makes pump selection different from simple aquarium turnover calculations because the pump must overcome vertical lift and hydraulic resistance while the aquatic zone may contain only a small volume of water.

The design sequence should be:

1. Measure the actual net aquatic-zone volume.
2. Select a suitable starting circulation rate.
3. Calculate the vertical lift and hydraulic resistance.
4. Calculate total operating head.
5. Read the manufacturer's pump curve at that operating head.
6. Verify the delivered flow.
7. Add flow control or a bypass if necessary.
8. Design intake geometry, evaporation reserve, heating, biological filtration, and service access around the selected equipment.

Circulation, mechanical filtration, biological filtration, and heating are separate functions. One piece of equipment may perform multiple functions, but a pump should not automatically be treated as a filter, and a false bottom should not automatically be treated as biological filtration.

Calculate the Aquatic-Zone Water Volume

Begin with the water the aquatic portion actually contains rather than the enclosure's external dimensions. Land structures, false bottoms, rocks, wood, substrate, dividers, and other permanent structures can substantially reduce usable water volume.

Use the paludarium water volume calculator to estimate the aquatic-zone volume before selecting the pump.

A useful starting calculation is:

Target circulation (L/h) = Net aquatic-zone volume (L) × chosen turnover rate (1/h)

For example, a 20 L aquatic zone with a 5× starting turnover target gives:

20 L × 5 = 100 L/h delivered flow

A 10× starting target would give:

20 L × 10 = 200 L/h delivered flow

These values describe desired delivered circulation. They do not mean that a pump advertised at 100–200 L/h at zero head will necessarily provide that flow after lifting water through the actual plumbing. The appropriate turnover depends on aquatic inhabitants, biological load, filtration, return geometry, and desired water movement, so 5×–10× should be treated as a starting design range rather than a universal requirement.

Calculate Total Operating Head

The pump must overcome more than vertical height. Include static lift and the major sources of hydraulic resistance.

H_total = H_static + H_friction + H_fittings + H_filter + H_outlet

Where:

• H_static is the vertical distance from the reservoir's operating water surface to the highest discharge point.
• H_friction represents resistance through tubing or pipe.
• H_fittings represents losses from elbows, tees, valves, reducers, and other fittings.
• H_filter represents resistance through filters, prefilters, or other restrictive equipment.
• H_outlet represents resistance from drip walls, spray bars, narrow returns, nozzles, or similar outlets.

For an open reservoir feeding an open return, do not automatically use the enclosure's total height as static head. Measure the vertical rise from the actual operating water surface to the relevant discharge elevation.

For example, if the reservoir water surface is 10 cm above the base and the waterfall outlet is 60 cm above the base:

H_static = 60 cm - 10 cm = 50 cm = 0.50 m

The final operating head will be higher if tubing, fittings, filtration, or the outlet create additional resistance.

Use the Pump Curve Instead of the Zero-Head Rating

A pump's advertised maximum flow is commonly measured at or near zero head. That value is useful for comparing equipment, but it is not necessarily the flow the pump will deliver after lifting water through the finished paludarium.

Use the manufacturer's pump curve as the primary sizing information. Find the flow available at the calculated operating head and compare that value with the required delivered flow.

For example, a pump advertised as:

800 L/h @ 0 m

must not be assumed to deliver 800 L/h when the system requires:

0.55 m operating head

Instead, read the manufacturer's curve at approximately 0.55 m and use that flow as the relevant operating value.

Do not apply a universal 50–70% loss assumption to every pump. Small submersible pumps can lose a substantial portion of nominal flow under meaningful lift, but the actual reduction depends on pump design, tubing diameter, fittings, filter resistance, outlet restriction, and operating conditions. The manufacturer's curve is more useful than a generic percentage.

The sizing test is:

Pump-curve flow at H_total ≥ required delivered flow

Paludarium Pump Sizing Workflow

Use this sequence when selecting a pump:

Operating-Head Sizing Example

Prevent Vortexing and Air Ingestion in Shallow Water

Shallow paludarium basins create an intake problem that differs from a conventional deep aquarium. In an 8–12 cm basin, an intake placed close to the surface can pull the water downward and form a surface vortex. Once air enters the intake, flow can become unstable and the pump can operate outside its intended conditions.

The immediate problem should be described as surface vortexing and air ingestion rather than assuming every shallow-water intake problem is classical cavitation. Cavitation and air ingestion are related but different hydraulic phenomena.

For shallow systems, prefer a low-profile or bottom-oriented intake where the pump and manufacturer-approved intake geometry permit it. Use a larger-area coarse prefilter to reduce localized suction velocity and protect the impeller from debris.

Where the false-bottom architecture allows it, create a dedicated pump sump or excavated pump chamber below or adjacent to the visible basin. This can provide greater effective intake depth while keeping the equipment accessible. The pump must still remain submerged to the depth specified by its manufacturer.

Keep the intake away from falling water and other areas where air is continuously entrained. Do not place a small intake immediately below a waterfall return.

Establish a minimum pump-safe water level and design the reservoir, sump, or top-off system so normal evaporation cannot expose the intake.

Integrate the Pump Chamber, Heater and Biological Media

The pump chamber can provide a compact equipment service area, but it should remain hydraulically open enough for reliable water replenishment and physically accessible for maintenance.

A practical equipment sequence is:

Reservoir / aquatic zone
↓
Accessible mechanical prefilter
↓
Pump chamber
↓
Pump
↓
Return plumbing
↓
Waterfall / stream / return

A compact heater can be installed in a continuously flooded pump or equipment chamber when the chamber provides adequate water movement and the heater manufacturer permits that installation. The heater must remain fully submerged and must not be allowed to operate partially exposed because evaporation has lowered the water level.

LECA, lava rock, or similar porous media can provide biological-media surface area when water actually passes through the media. Filling a false bottom with LECA or lava rock does not automatically make it an effective biological filter. A stagnant or poorly circulated media bed may function primarily as drainage or structural space.

A hollow false bottom with little water movement is primarily a drainage/reservoir structure. A controlled-flow LECA or lava-rock bed can provide biological filtration when appropriately connected to the water path. A dedicated filter chamber or media basket provides a more predictable and serviceable biological-media arrangement.

Reduce Plumbing Friction With Appropriate Tubing

Tubing friction can consume a significant portion of a small pump's available head, particularly when a builder combines a long narrow tube with multiple sharp fittings. The problem becomes more important when the return rises 45–60 cm or includes a drip wall, waterfall, filter, valve, or manifold.

As a practical baseline, use approximately 12 mm internal diameter for the main return line where the pump and fittings support that size. This is a design guideline rather than a universal minimum. Larger tubing can be appropriate when the pump, flow requirement, and plumbing architecture justify it.

Do not treat 8–9 mm ID tubing as automatically unusable, but recognize that smaller internal diameter increases water velocity and can increase friction loss at a given flow. A narrow line can therefore consume a disproportionate share of the pump's available head.

Prefer sweeping tubing bends and long-radius fittings where practical. Minimize unnecessary sharp 90-degree elbows, repeated barbed elbows, tees, reducers, and sudden internal-diameter changes.

A single 90-degree elbow is not inherently a problem. The issue is cumulative minor loss when many restrictive fittings are combined with narrow tubing and significant vertical lift.

Solve the Tall-Tank and Small-Basin Flow Problem

A tall paludarium can require substantial head pressure while its aquatic zone may contain only 15–30 L. A pump powerful enough to reach a high waterfall can therefore create excessive current when connected directly to the aquatic return.

The key distinction is:

Head requirement ≠ desired biological flow

For example, a 20 L aquatic zone with a 5× starting circulation target requires:

20 L × 5 = 100 L/h delivered flow

If the return requires 0.60 m of operating head, the pump must be capable of producing approximately 100 L/h at that operating head. A pump capable of substantially more flow at that operating head may require output control or flow splitting.

Adjustable-output pumps are useful when the pump curve provides adequate head capability but unrestricted flow is excessive.

A discharge-side valve can be used for flow adjustment where the pump manufacturer permits it. Do not routinely restrict the pump's suction/intake side to control flow. Suction restriction can promote intake starvation and abnormal operation.

A bypass or T-junction can be useful when the pump needs substantial head capability but the aquatic system requires gentle flow:

Pump
  |
  +----> Main waterfall/drip return
  |
  +----> Bypass back to reservoir

A manifold can similarly divide flow between a waterfall, stream, spray return, and direct reservoir return. Bypass flow adds plumbing and recirculation, so it should be used deliberately rather than treated as automatically superior to correct pump selection.

Calculate an Evaporation Buffer for a Shallow Basin

Waterfalls, exposed water surfaces, ventilation, room conditions, and strong terrestrial lighting can increase evaporation. In a shallow 10–20 L aquatic zone, even a small vertical drop can represent a significant fraction of total water depth and can bring the pump intake dangerously close to the surface.

Calculate the water volume represented by an allowable water-level drop using exposed water surface area:

Evaporation buffer (L) ≈ A × D

Where A is exposed water surface area in square metres and D is the allowable water-level drop in millimetres.

The relationship works because:

1 m² × 1 mm = 1 litre

For example, with 0.20 m² of exposed water surface and a 20 mm allowable drop:

0.20 × 20 = 4 L

The 4 L is the geometric volume represented by that level drop. It is not a prediction that exactly 4 L will evaporate in a particular number of days. Actual evaporation depends on surface area, temperature, humidity, ventilation, waterfall splash, enclosure design, and lighting.

Define three operating levels:

• Maximum operating level: the upper fill boundary.
• Normal operating level: the preferred day-to-day level.
• Minimum pump-safe level: the lowest level allowed before pump protection or top-off intervention.

If a 2 cm drop would expose the intake or cause vortexing, do not rely on a fixed calendar interval for topping up. Build enough reserve, monitoring, or automatic top-off capacity to keep the water above the minimum pump-safe level during the intended unattended period.

Place Low-Water Sensors and ATO Controls Correctly

A low-water sensor or automatic top-off sensor should monitor the water level that actually determines pump safety rather than simply the visually preferred level in the display area.

If the pump is installed in a dedicated chamber whose water level accurately tracks the main reservoir, the sensor can be located in that chamber. The sensor should sit in a relatively calm area rather than directly beneath a waterfall or beside turbulent return flow.

Avoid placing the sensor where surface waves, splash, algae, debris, or an isolated chamber can produce false readings. The sensor chamber must represent the water available to the pump.

Where supported by the equipment, an independent low-water cutoff provides an additional layer of protection. The cutoff should be treated as protection against unsafe low-water conditions, not as a substitute for maintaining the correct normal water level.

Automatic top-off should replace evaporation, not compensate indefinitely for leaks. If the system consumes substantially more top-off water than expected, inspect for leaks before increasing the ATO reservoir.

Canister Filters in Low-Water Paludariums

External canister filters can be used in paludariums, including compact systems with integrated-heater designs, but shallow reservoirs make intake depth and priming less forgiving than in a conventional deep aquarium.

A canister depends on a continuously flooded intake path and an intact priming or siphon arrangement. The intake should remain submerged at the minimum operating water level, be protected against surface vortexing, and be kept away from waterfall splash and other sources of continuous air entrainment.

A shallow basin can lose a large percentage of its depth through a small evaporation drop. If the intake approaches the surface, vortexing or air ingestion can introduce air into the intake path and, depending on the canister design, contribute to reduced flow or loss of prime.

Before relying on a canister system:

1. Position the intake below the minimum operating water level.
2. Use an accessible intake prefilter.
3. Route hoses to minimize unnecessary high points where air can accumulate.
4. Keep hose and fitting connections airtight.
5. Follow the manufacturer's priming procedure.
6. Perform a controlled power-interruption test to verify restart behavior.
7. Test operation at the minimum intended water level.
8. Provide appropriate low-water protection.

A canister filter does not remove the need to solve the underlying shallow-reservoir hydraulic problem.

For integrated-heater canisters, the reduced equipment footprint can be useful, but the heater still requires the manufacturer's specified water level, circulation, installation conditions, and service access. Do not assume that every canister has identical priming, restart, heater, or low-water behavior.

Build the Pump Into the Hardscape Without Losing Service Access

Serviceability is a construction requirement, not an optional convenience. Before the false bottom, foam, rocks, wood, substrate, or waterfall is permanently installed, establish a physical path for removing the pump and mechanical prefilter.

Never permanently foam, silicone, rock, substrate, or hardscape a pump into the false bottom.

A preferred service architecture is:

Removable hatch
↓
Access shaft
↓
Mechanical prefilter
↓
Pump chamber
↓
Tubing / return line

The pump should be removable without dismantling the paludarium. The access opening should be large enough to remove the actual pump and intake assembly, not merely large enough to see them.

Where appropriate, use disconnectable tubing connections and removable intake guards or prefilters. Keep loose substrate out of the pump chamber so routine cleaning does not disturb the terrestrial substrate bed.

Hardscape should be designed around the service path. A waterfall that requires demolition to reach a clogged impeller is a mechanically poor installation.

Coordinate this equipment architecture with the step-by-step paludarium build guide, which covers enclosure selection, terrain structure, drainage, hardscape, water systems, lighting, planting, testing, and stabilization.

Separate Circulation From Filtration

A pump moves water. A filter provides mechanical and/or biological treatment. Circulation distributes water and supports oxygen and heat transfer. These functions can be combined in some equipment, but they should remain conceptually separate during system design.

Mechanical filtration catches suspended debris before it reaches the pump or biological media. Biological filtration provides surfaces where microbial communities can process dissolved nitrogenous waste. A false-bottom LECA or lava-rock bed can contribute biological filtration only when the system actually routes water through it.

A lightly stocked planted system and a fish-bearing aquatic zone should not automatically receive the same filtration architecture. Required filtration depends on aquatic volume, bioload, planting, water movement, substrate design, and intended livestock.

When a mechanical prefilter is used, keep it accessible enough to clean before restriction causes the pump to lose flow. A clogged prefilter changes the hydraulic operating point and can undermine a pump-sizing calculation that was correct when the system was clean.

Diagnose Low Flow, Vortexing and Pump Problems

If delivered flow is lower than expected, troubleshoot the system logically rather than immediately replacing the pump.

1. Confirm the actual water level and verify that the intake remains safely submerged.
2. Inspect the mechanical prefilter for blockage.
3. Check the intake for debris and surface vortexing.
4. Confirm the pump is installed according to the manufacturer's requirements.
5. Inspect tubing for kinks, trapped air, or accidental restrictions.
6. Check sharp fittings, reducers, valves, and outlet restrictions.
7. Confirm the measured vertical lift matches the original operating-head calculation.
8. Inspect the impeller and pump chamber according to the manufacturer's maintenance procedure.
9. Compare the expected operating point with the manufacturer's pump curve.
10. If the system has a canister, verify that the intake remains flooded and the filter has not lost prime.

Do not solve a low-flow problem by blindly increasing pump size. A larger pump can increase current, heat, noise, or intake problems in a small aquatic zone. First determine whether the lost flow is caused by maintenance, plumbing friction, excessive outlet restriction, insufficient intake depth, or incorrect pump selection.

Paludarium Filter and Pump Setup Checklist

• Measure actual net aquatic-zone volume rather than relying on enclosure dimensions.
• Select a design turnover rate appropriate to the aquatic system.
• Calculate required delivered flow from Volume × turnover.
• Measure static lift from the operating water surface to the highest return point.
• Include tubing, fittings, filter, and outlet resistance in H_total.
• Select the pump using its operating-head curve rather than its zero-head rating.
• Use approximately 12 mm ID as a practical main-line baseline where compatible, especially for taller or higher-resistance runs.
• Prefer sweeping bends and minimize unnecessary sharp elbows, tees, and sudden ID reductions.
• In 8–12 cm basins, use low or bottom-oriented intake geometry and an accessible coarse prefilter where compatible.
• Keep the intake away from waterfall splash and air-entraining turbulence.
• Establish maximum, normal, and minimum pump-safe water levels.
• Calculate evaporation buffer using A × D, with area in m² and allowable level drop in mm.
• Place low-water sensors where they represent the water level available to the pump.
• Use discharge-side flow control, adjustable output, or a bypass when high-head capability would otherwise create excessive current.
• Do not routinely restrict the pump's suction side to control flow.
• If using LECA or lava rock as biological media, ensure water actually passes through the media.
• Keep mechanical filtration, pumps, heaters, and tubing serviceable.
• Never permanently foam or hardscape a pump into the false bottom.
• If using a canister, keep the intake below the minimum operating level and test priming and restart behavior.
• Follow the manufacturer's requirements for pump minimum depth, heater placement, canister installation, priming, and maintenance.
• Leak-test and power-cycle the completed system before introducing livestock.
• Recheck actual flow after installation and after filters or prefilters have accumulated debris.