Let gravity take the heavy solids first.
A settler slows the water so heavy particles drop out before they reach the drum filter. Below: what it removes, which type to use, how it is sized and when you do not need one.
removed by gravity
in the settling zone
in the loop
drawn off on a routine
Slow water, falling solids.
Solids from the tank drain are a mix of heavy faeces, uneaten feed and fine particles. A settler lowers the water speed so the heavy fraction sinks and can be drawn off as thicker sludge. In a 2025 freshwater trout trial, a swirl separator ahead of the drum filter removed the most organic matter per day of the four set-ups tested ().Aquacultural Engineering, 2025
- heavy, fast-settling solidsRemoves:
- fine and light particles. They go on to the drum filter and, where used, the skimmer.Leaves:
- improve water quality on its own as much as foam fractionation. In the same trial, removing more solids did not by itself give the clearest water.Does not:
Swirl separator or radial-flow settler.
The two common types work differently, and their removal differs. In one comparison, mean suspended-solids removal was about 37% for a swirl separator and about 78% for a radial-flow settler ().radial-flow settler study
Swirl separator
Water enters tangentially and spins; solids collect at the centre of the base
Compact; handles the bottom-drain flow from dual-drain tanks
Removes less of the total solids
Radial-flow settler
Water enters at the centre and flows slowly outward; solids settle
Higher solids removal
Larger for the same flow
Plate or tube settler
Inclined plates shorten the distance particles fall
Small footprint for its area
Plates need cleaning
Slow enough for the particles to fall.
A settler works when water rises through it more slowly than the particles sink. That sets its surface area.
Flow to treat
Often only the bottom-drain flow from dual-drain tanks, which carries most of the heavy solids in a small share of the water.
Particle settling speed
Heavy faeces and feed sink fast; fines sink slowly. The settler is sized for the particles it is meant to catch.
Surface loading
Flow divided by surface area must stay below the settling speed of those particles.
Sludge removal
Drawn off before it breaks down, or it releases nutrients back into the water.
Where a settler earns its place.
High feed loads, dense grow-out
Often yes: it takes load off the drum filter
Dual-drain tanks
Often yes: a swirl separator treats the concentrated bottom flow
Sludge to be thickened or reused
Yes: thicker sludge is easier to handle
Low feed load, single drain
Usually not: the drum filter handles it
Fine particles and colour are the problem
No: a skimmer, often with ozone, addresses that
When the settler stops working.
Solids carried over to the drum
Flow above design, or sludge not drawn off
Flow; sludge level and draw-off routine
Nutrients rising
Sludge left too long, breaking down
Draw off more often
Sludge line blocked
Draw-off too infrequent, sludge too thick
Draw-off frequency; valve and line
Little sludge collected
Flow too fast, or particles too fine to settle
Surface loading; feed and particle type
A settler only where the numbers show it helps.
We size the settler with the drum filter and skimmer, so solids removal is split across them the right way.
Sized on your load
Flow, feed and the solids it is meant to catch.
Matched to the drum
Settler and drum filter sized together.
Material for your water
Confirmed against your salinity in the quote.
Fitted and tested
Supplied, fitted and tested with the rest of the system.
Standard specification.
Function
Removes settleable solids by gravity
Type
Swirl separator or radial-flow, confirmed per project
Material
Confirmed against water type and salinity
Position
Between tank drains and drum filter
Sizing
On flow and solids load
Lead time
Standard units 15 days
Model dimensions and connections are listed in the datasheet. We confirm the model against your flow before quoting.
Not always. On high feed loads a settler cuts the load on the drum filter. We recommend one when the numbers show it helps.
A swirl separator is compact and suits the bottom-drain flow from dual-drain tanks. A radial-flow settler removes more solids but needs more space.
From the bottom of the settler, through a drain valve, on a routine your team follows. Drawing it off often keeps nutrients from leaking back into the water.
It takes the heavy solids. Clear water depends more on the drum filter and, in dense systems, a skimmer.
Yes. We choose the material against your salinity and confirm it in the quote.
Send your flow and feed. We size the filtration line.
Tank layout, drain type, peak flow and peak daily feed.
- Settler only where it helps
- Sized with the drum filter
- Material for your water
- Standard units ship in 15 days