Biofloc and Land-Based Fish Farming: How to Size and Specify Aquaculture Tanks

Biofloc fish farming is a water-treatment approach used inside a land-based tank, where a microbial community is kept suspended and aerated. The tank is a container on land: a frame or wall, a flexible liner, an outlet, and a water supply the farm controls. Ponds rely on soil, sunlight and natural processes; cages sit in a lake, river or sea. A tank gives the farm control over volume, depth, drainage and aeration interfaces, and it puts the cost of pumping and treatment on the farm.

That difference matters. Pond construction costs and water control depend on the site. A cage borrows the water body and inherits its risks. Land-based tanks hold a defined volume that can be measured, drained and isolated between cycles, which supports separate management of production cycles. Biofloc fish farming adds one more requirement: the tank keeps the floc suspended and aerated while letting excess solids leave through a drain. The tank specification follows the system specification, never the other way round.

The table maps three land-based approaches to their tank requirements.

In a biofloc tank, bottom aeration keeps particles suspended, and rounded layouts help avoid dead zones where sludge settles; the drain is purged periodically rather than run at a high continuous flow. In a RAS, mechanical filters and biofilters treat recirculated water; a circular tank can use rotational flow to move solids toward a central outlet. In flow-through, the risk is short-circuiting, where clean water exits out the drain, so overflow and outlet pipes must pass peak flow without backing up the water line.

The order matters: a tank bought before the system is designed fits aeration and solids removal into leftover space. A RAS that leaves the sump and return manifold until later loses floor space and hydraulic head it cannot recover. Flow-through is limited by its source, so tank size follows the available flow, not the other way round. Settle the system first, then write the tank specification against it.

FUUSHAN supplies the tank structure and liner. Filtration, aeration, pumping and biological design belong to the project's specialists. Our aquaculture and biofloc tank configurations overview covers the rest.

Start with the plan the farm already has. An aquaculture consultant sets the target biomass in kilograms and the stocking density the system can support, usually in kilograms per cubic metre. Total water volume follows from those two numbers:

The density figure is the specialist's decision, not a tank supplier's. It depends on species, dissolved oxygen, aeration, filtration, feeding and climate, and changes as fish grow from fingerlings to harvest weight. No fixed litres-per-fish figure is published here, because a generic guess rarely survives the first hot week or a peak feeding period.

Two adjustments follow when calculating a biofloc fish tank size or RAS holding capacity. Working volume is lower than geometric volume, because the water line sits below the wall top to leave freeboard for surface agitation. Splitting the total across independent tanks lets cohorts, grading, treatments and cleaning be staggered. The formula uses operating water depth; geometric volume uses full wall height. A sloped or conical floor adds volume below the wall base, counted separately.

Biomass is not static. Fish grow, cohorts split as density rises, and a plan that fits in month one may need full capacity by month six. Size for peak standing biomass before harvest, and keep floor room to add tanks.

Two rules keep the geometry honest. Keep the water line below the wall top, because freeboard absorbs waves from heavy aeration and keeps the liner from loading at the rim. Check the footprint early: tank diameter plus walkways, drain trenches and pipe corridors often decides the layout before volume does, especially when indoor columns or site access are tight.

Diameter drives footprint and rotational velocity; depth drives hydrostatic pressure and blower backpressure; tank count drives batching, biosecurity isolation and the number of outlets. A wide, shallow tank behaves differently from a narrow, deep one at the same volume: deep water needs more blower pressure and makes netting harder, while shallow water takes more land and reacts faster to ambient temperature. Confirm the combination with the supplier and the system designer, because wall height, ring spacing, base preparation and aeration layout follow from it.

This section is a summary; for a side-by-side breakdown, compare all three tank structures.

The structures differ in site handling. Bolted panels are assembled ring by ring and treated as semi-permanent; pipe frames arrive as tube bundles and clamp together; folding tanks collapse into a bundle when drained. Base preparation and assembly time differ with structure and soil. The right choice follows from site access, permanence and how often the tank moves.

Each structure page states its own reference range, and final dimensions are confirmed per project.

In all three designs, the frame or steel wall carries the load while the liner holds the water. The liner stays in contact with the culture water, the stock and the bottom aeration hardware.

The flexible PVC panels are thermally welded into a tailored bag that matches the frame geometry, and seam continuity is inspected at the factory before packing; our quality control and seam inspection covers what is checked. Seam integrity is verified before dispatch.

In the field, mechanical damage during setup can cause early liner trouble. A liner pinched between a steel panel and rough ground, abraded by unshielded diffuser weights, or stretched over an unpadded rim will wear prematurely. A protective geotextile underlay, padding on the top edge of steel panels and a little slack in the bottom corners are common site practices, confirmed per project where used.

Many delays come from a scope line never drawn between the container supplier and the system integrator. Three interfaces need clear ownership before manufacturing starts.

Who does what. FUUSHAN supplies the tank structure, the flexible PVC liner, the agreed outlets and valves, and assembly guidance. The farm or its contractor prepares the ground and assembles the tank. The system specialist handles equipment integration, biological start-up, and water treatment and aeration design. A six-line matrix covers it: base works, tank and liner, assembly guidance, on-site labour, treatment and aeration, start-up. Each line gets one owner.

The foundation decides whether the tank stands plumb and spreads the load. The ground must be level, compacted and stable, able to bear the filled tank without differential settlement, with perimeter drainage that keeps rainwater out of the sub-base. Depending on structure, diameter and soil, the base is typically a compacted sand pad with a curb or a level reinforced concrete slab, confirmed per project. Where a central bottom drain is used, the sub-floor pipe and elbow are typically trenched and backfilled flush before the wall goes up. A soft or uneven base shows up as an out-of-round wall or a strained liner.

Materials arrive packed, so the farm needs vehicle access and dry staging away from sharp debris. Packed dimensions and weights are confirmed after packing, not from a drawing; our guide on export packing and delivery explains.

Assembly follows a fixed sequence: verify base level and drain alignment, erect the frame or panel wall, lay the underlay and edge protection if the project specifies them, position the liner, fit the outlet and fittings, then run a shallow test fill to check valve seals. FUUSHAN provides assembly guidance. The crew is the farm's or its contractor's, and the system specialist handles biological start-up; on-site installation labour and commissioning are outside our scope.

The quotation is only as accurate as its inputs. Prepare these ten items before you send an enquiry:

1. System type: biofloc, RAS, flow-through, nursery, quarantine or temporary holding.
2. Stocking context: target species, the consultant's density plan and peak biomass.
3. Capacity or geometry: working volume per tank, or the diameter, length, width and depth you have in mind.
4. Tank count and layout: total tanks and how cohorts will be split.
5. Water chemistry: freshwater, brackish or seawater, plus whether the site is coastal or exposed to high ambient temperatures.
6. Site and foundation: indoor warehouse or outdoor yard, soil or base type, and unloading access.
7. Drain and valve: central bottom drain or side outlet, pipe diameter, flange or thread standard and valve preference.
8. Auxiliary ports: inlets, skimmers, overflow pipes, standpipes and sensor access.
9. Logistics: destination port or country, Incoterms and container or crating constraints.
10. Project schedule: target delivery window so factory slots and ocean freight can be planned.

Missing items become assumptions that later trigger redesigns and price revisions. Submit the checklist when you send your tank requirements, and the structure, liner and port configuration can be reviewed before a price is issued.