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PUREFLOW BIO / ENGINEERING FIELD GUIDE

Biofilter Start-Up and CyclingHow Long and What to Watch

How to start a new biofilter, what the ammonia and nitrite curve looks like, and how to speed up cycling safely.

Explore the process ↗Open the workbench
6 MIN GUIDEUPDATED NOVEMBER 2026
Reference illustration for Biofilter Start-Up and Cycling: How Long and What to WatchEQUIPMENT REFERENCE
Equipment reference illustration. Confirm the supplied model configuration and installation arrangement from its approved documentation.
01Understand the mechanismInspect the relevant process stages.
02Review the operating dutyKeep assumptions and measured values visible.
03Prepare the next decisionUse the guide, tools and project checks.
INTERACTIVE PROCESS ATLAS

See the mechanism.
Understand the duty.

Select a route or a stage to inspect the process. The cutaway explains the equipment and water environment; it is a teaching illustration, not a project drawing.

Swipe horizontally to inspect the equipment. Stage buttons below also centre the selected component.
Aerated biological treatment and samplingPUREFLOW / INTERACTIVE PROCESS ATLASCONCEPT LAYOUT · NOT TO SCALETAN-NpH°CPRE-SCREENED SUPPLYBIOFILM ON MOVING CARRIERSMEASURE THE PROCESSAIR DISTRIBUTIONNH₄⁺ → NO₂⁻ → NO₃⁻Motion explains the process; it is not a measured flow rate or biological time model.
Pre-screened water reaches the biological stage and continues through the retained-media outlet.
Selected process stage

Feed the reactor

Define peak feed and the nitrogen load.

How it works

Pre-screened water enters the biological stage. Effective upstream solids removal helps protect the reactor.

What to establish
  • Define peak feed and the nitrogen load.
  • Check oxygen, pH, alkalinity and temperature.
  • Use supported media performance and the specified fill arrangement.

Continue this guide ↗

Motion explains direction and mechanism; it does not represent measured performance. Geometry, stage order, pipe routes and equipment configuration are conceptual. Use the approved project design, operating instructions and verified model data.

Key takeaways

  • The usual pattern: First ammonia rises and then falls as one group of bacteria grows.
  • How to start: Run the filter with water at the right temperature and plenty of oxygen.
  • Speeding it up: Seed it with media or water from a healthy, established filter.
  • Stocking: Add fish gradually after cycling, and increase feed in steps so the biofilter can catch up.
Reference illustration for Biofilter Start-Up and Cycling: How Long and What to Watch
Equipment reference visual; not evidence of a completed installation.
THE SHORT ANSWER

The usual pattern

First ammonia rises and then falls as one group of bacteria grows. Nitrite then rises and falls as a second group follows. When both stay at zero while you add an ammonia source, the filter is cycled. It often takes several weeks, faster in warm water.

Biofilter Start-Up and Cycling - Pureflow Bio
Reference visual. Equipment configuration and project details must be confirmed separately.
BIOFILTERS

How to start

Run the filter with water at the right temperature and plenty of oxygen. Add a small ammonia source, either a little feed or pure ammonia, and test every day or two.

PLANNING WORKBENCH

Work with your own numbers.

Use the tools below to explore the relevant arithmetic. Enter measured values or declared assumptions. An estimate does not establish equipment capacity, biological performance or a safe operating limit.

Biofilter media planning scenario

Relate a defined nitrogen load to an explicitly supplied media conversion rate and fill share.

Assumptions and limits

Use a conversion rate verified for the media, water chemistry, oxygen, temperature and load. Example numbers are arithmetic inputs, not approved biological capacities or fill recommendations.

—TAN-N load · g/day
—Media volume · m³
—Nominal reactor volume · m³
Enter your values, or load the labelled arithmetic example. No design values are pre-filled.
FormulaMedia m³ = feed × TAN-N yield ÷ conversion rate. Reactor m³ = media m³ ÷ fill fraction.
Convert units before you calculate
Choose units and enter a value.

Planning arithmetic · inputs remain visible for review · example values are not operating recommendations

BIOFILTERS

Speeding it up

Seed it with media or water from a healthy, established filter. Keep alkalinity up, because bacteria use it. Do not use chlorinated water or medicines that kill bacteria.

BIOFILTERS

Stocking

Add fish gradually after cycling, and increase feed in steps so the biofilter can catch up. See sizing.

BIOFILTERS

Common mistakes

Stocking fully on day one, switching off aeration, and cleaning media with tap water.

Pureflow Bio equipment for this

MBBR biofilters →Moving bed biofilters.Standard drum filters (RDF) →Automatic solids removal.
PROJECT REVIEW

Check the biological assumptions

Use these questions to prepare a project brief or an operating review. Check an item only when the information has been recorded for your installation.

0 of 3 checked

This checklist is a working aid in the current page session, not a saved maintenance record.

QUESTIONS

Biofilter Start-Up and Cycling FAQ

How long does it take?

Commonly four to six weeks, shorter if you seed it.

Can I cycle with fish in?

It is possible with very light stocking and careful testing, but it is harder on the fish.

KEEP READING
Biological filters→MBBR biofilters→Water quality→Biofilter Media Types: Plastic Carriers, Sand, Ceramic and Brushes ↗How to Size a Biofilter: TAN Load, Media and Reactor Volume ↗

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