Pureflow Bio library
Keeping water clean, without the guesswork
We build filters and water treatment equipment in India. This library holds the things we end up explaining to customers again and again: how to size a system, what usually goes wrong, and what to check before you spend money.
How fast should water move through your filter?
Put in your pond or tank volume and see the flow you should plan for. Includes the reasoning, so you can judge the number rather than just trust it.
Subjects
Pick what you are working on
Koi ponds
Building a pond that stays clear, picking a filter, and the routine that keeps it that way.
- Koi Pond Filter Size: How to Size a Filter for Your Pond
- Green Pond Water: Causes and How to Clear It
- Cloudy Pond Water: Causes and Fixes
Natural swimming pools & ponds
Pools you can swim in without chlorine, kept clean by plants and filters.
- Natural Swimming Pools: How Biological Pool Filtration Works
- Swimming Pond Filters: Choosing Mechanical and Biological Filtration
- Natural Ponds: Design for Clear Water and Wildlife
Aquaculture & RAS
Starting a farm, how recirculating systems are put together, and notes on common species.
- Recirculating Aquaculture Systems (RAS): Design and Equipment Guide
- Drum Filter for Aquaculture: Solids Removal in Fish Farms and RAS
- Aquaculture Filtration Systems: Mechanical, Biological and Disinfection
Aquaponics
Growing fish and vegetables together, and keeping the balance right.
- Best Fish for Aquaponics: Choosing the Right Species
- Aquaponics: How It Works and Is It Right for You
- Fish to Plant Ratio in Aquaponics: How to Balance Your System
Hydroponics
Growing in nutrient water instead of soil, and keeping that water healthy.
- Hydroponics: Systems, Nutrients and Water Treatment
- Drum Filter for Hydroponics: Cleaner Recirculating Solution
- Recirculating Hydroponics: Save Water and Control Disease
Aquariums
Everything from a home tank to a public display, plus quarantine and breeding setups.
- Drum Filter vs Sump: Which Suits Your Aquarium?
- Aquarium Drum Filter: When and How to Use One
- Aquarium Filtration: Mechanical, Biological and Chemical Stages
Water quality
What to test, what the numbers mean, and what to do when they go wrong.
- Water Quality for Fish: Ammonia, Nitrite, pH and Oxygen
- Ammonia Toxicity and pH: Why the Same Reading Can Be Safe or Deadly
- Dissolved Oxygen in Fish Systems: Targets, Drops and Fixes
Drum filters
How drum filters work, which mesh to choose and what to do when they misbehave.
- Drum Filter Troubleshooting: Causes and Fixes
- Drum Filter Mesh Size: How to Choose the Right Micron Screen
- Rotary Drum Filter (RDF): How It Works and Where to Use It
Biofilters
How bacteria clean the water, and the filter designs that give them a home.
- Biological Filters: Nitrification, Media and Sizing
- Moving Bed Biofilters (MBBR): Design and Operation
- Trickle Filters: Biological Filtration and Degassing in One
UV-C systems
Using UV light against algae and germs, and looking after the lamp.
- UV System for Ponds, Aquariums and Aquaculture
- UV Clarifier vs UV Sterilizer: Is There a Real Difference?
- UV Lamp Sizing and Dose: How to Pick the Right UV Unit
Ozone systems
What ozone can do for water, and the safety side you must not skip.
- Ozone System for Aquaculture and Aquariums: How It Works and Safety
- Ozone and ORP Control: Dosing Without Guesswork
- Ozone Safety: Destruct Units, Ventilation and Residual Ozone
Water circulation pumps
Picking a pump that moves enough water without wasting power.
- Water Circulation Pumps: How to Choose for Ponds and Aquaculture
- Pump Head Loss and Pipe Sizing: Why Your Flow Is Lower Than Expected
- Airlift vs Pump Circulation: Moving Water Cheaply and Gently
Gravity-fed or pump-fed
Letting gravity do the work, or pushing water with a pump.
- Gravity-Fed or Pump-Fed Filters: Which Is Better?
- Gravity-Feed Pipework Design: Slopes, Levels and Air Locks
- Sump and Pump Station Design: Where the Clean Water Goes
Turnover rate
Working out how much flow your pond or tank needs.
- Turnover Rate: How to Calculate It for Ponds, Tanks and RAS
- Turnover Rate and Biofilter Contact Time: Faster Is Not Always Better
- Turnover Rate by System Type: Ponds, Aquariums, RAS and Natural Pools
If you are new to this
A sensible order to read things in
Most people read about UV or ozone first and only later realise their solids are the real problem. These six follow the order a system actually works in.
Start with water quality
Ammonia, nitrite, pH and oxygen: what to test and why.
Work out your flow
Turnover time sets pump and filter size. Use the calculator.
Remove solids
How a rotary drum filter protects the rest of the system.
Treat dissolved waste
Biofilter types, media and sizing from feed load.
Control algae and pathogens
UV sizing, dose and lamp care.
Put it together
See how every stage fits in a recirculating system.
Everything we have written
All articles
Cloudy Pond Water: Causes and Fixes
Find out why pond water is cloudy white, brown or milky, and how to fix it with filtration, water changes and cycling.
Drum Filter vs Other Pond Filters: Which Is Best for Koi?
Compare drum filters, settlement chambers, vortex, sand and bead filters for koi ponds by solids removal, upkeep and cost of running.
Green Pond Water: Causes and How to Clear It
Why pond water turns green, how nutrients, sunlight and filtration contribute, and how UV, filtration and maintenance clear it.
How to Build a Koi Pond: Step-by-Step Planning Guide
Plan and build a koi pond: location, depth, shape, bottom drain, filtration and testing before adding fish.
Koi Pond Bottom Drain: Why You Need One and How to Fit It
What a bottom drain does, how many to use, sizing pipework and how it feeds a drum filter or settlement chamber.
Koi Pond Filter Size: How to Size a Filter for Your Pond
How to size a koi pond filter from pond volume, stocking, flow rate and turnover time, with a worked example.
Koi Pond Filters: Types, Stages and What to Choose
The main types of koi pond filter: mechanical, biological and UV stages, and how to combine them.
Koi Pond Maintenance: Daily, Weekly and Seasonal Checklist
A practical koi pond maintenance routine: water tests, filter care, feeding, cleaning and seasonal tasks.
Koi Ponds: Design, Filtration and Water Quality Guide
Everything about koi ponds in one place: depth, volume, filtration stages, water quality, stocking and equipment choices.
How to Build a Swimming Pond: Planning and Filtration
Plan a swimming pond: zones, depth, lining, circulation, filtration and commissioning.
Natural Ponds: Design for Clear Water and Wildlife
How to design a natural garden pond with plants, depth and gentle filtration for clear water and healthy wildlife.
Natural Swimming Pools: How Biological Pool Filtration Works
How natural swimming pools stay clean without chlorine, using plants, biofilters and mechanical filtration.
Swimming Pond Filters: Choosing Mechanical and Biological Filtration
Which filters a swimming pond needs: skimmers, mechanical screens, biofilters and UV, and how to size them.
Aquaculture Filtration Systems: Mechanical, Biological and Disinfection
A clear guide to aquaculture filtration: mechanical filters, biofilters, foam fractionation, UV, ozone and how to build a stage plan.
Catfish Farming: Systems, Water Quality and Equipment
What catfish need in tanks, ponds and RAS: oxygen, water quality, solids control and the equipment that supports intensive culture.
Drum Filter for Aquaculture: Solids Removal in Fish Farms and RAS
Why fish farms use drum filters, how to size by flow and feed load, and how they protect biofilters.
How to Start a Fish Farm: Planning Steps for India
Plan a fish farm: choose species, site, system type, water source, equipment, permits and a realistic production plan.
Recirculating Aquaculture Systems (RAS): Design and Equipment Guide
How a RAS works: solids removal, biofiltration, oxygenation, degassing and disinfection, with design points and equipment.
Shrimp Farming in RAS: Water, Biosecurity and Equipment
How RAS shrimp farming works: salinity, solids, biofiltration, biosecurity, aeration and the equipment that protects water quality.
Stocking Density in Aquaculture: How Many Fish per Tank
How stocking density is set by oxygen, filtration and growth stage, with a calculation approach for tanks and RAS.
Tilapia Farming: Water, Tanks and Filtration
Key conditions for tilapia: temperature, oxygen, tank and RAS design, and the filtration equipment that supports good growth.
Trout Farming: Cold Water, Oxygen and RAS Basics
Requirements for trout: cold clean water, high oxygen, flow-through versus RAS, and the filtration and oxygen equipment needed.
Aquaponics Filtration: Solids, Biofilters and Water Treatment
Which filters an aquaponics system needs: solids removal, biofiltration, aeration and UV, and how to size them.
Aquaponics vs Hydroponics: Differences, Costs and Which to Choose
Compare aquaponics and hydroponics on nutrients, skill, setup, risks and output to choose the right system.
Aquaponics: How It Works and Is It Right for You
A complete introduction to aquaponics: the nitrogen cycle, system types, fish and plants, and the equipment that keeps it stable.
Best Fish for Aquaponics: Choosing the Right Species
Compare tilapia, catfish, carp, trout and ornamental fish for aquaponics by temperature, hardiness and market.
Decoupled Aquaponics: Separate Fish and Plant Loops
What decoupled aquaponics is, why it gives better control, and how it is built and managed.
Fish to Plant Ratio in Aquaponics: How to Balance Your System
How to balance fish feed and plant area in aquaponics, with a feed-rate method and a worked example.
How to Build an Aquaponics System: Step-by-Step
Plan and build an aquaponics system: fish tank, solids filter, biofilter, grow beds, pumps and cycling.
Deep Water Culture: Setup, Oxygen and Common Problems
How deep water culture works, why oxygen matters, and how to avoid root rot and temperature problems.
Drum Filter for Hydroponics: Cleaner Recirculating Solution
Why large hydroponic farms use drum filters, what they remove, and how to size one for a recirculating system.
Hydroponics: Systems, Nutrients and Water Treatment
A complete guide to hydroponics: system types, nutrient management, EC and pH, water treatment and equipment.
Nutrient Solution EC and pH: Targets and How to Manage Them
What EC and pH mean in hydroponics, typical target ranges and how to adjust the nutrient solution.
Recirculating Hydroponics: Save Water and Control Disease
How recirculating hydroponic systems reuse nutrient solution, and how to filter, disinfect and rebalance it.
UV Sterilisation for Hydroponics: Protecting the Nutrient Solution
How UV-C reduces pathogens in hydroponic nutrient solution, how to size it, and what to check.
Aquarium Drum Filter: When and How to Use One
How an aquarium drum filter keeps large and public aquariums clear, where to fit it and what to check before buying.
Aquarium Filtration: Mechanical, Biological and Chemical Stages
How aquarium filtration works, the three stages, sizing by volume and flow, and when to add skimmers, UV and ozone.
Aquarium Rack Filtration: Shared Systems for Many Tanks
How rack systems share one filtration loop across many tanks, with design points, benefits and risks.
Breeding Tropical Fish: Water, Tanks and Filtration
What breeders need: stable water, gentle filtration, separate tanks and live food, with tips for egg-layers and livebearers.
Discus Breeding: Water Quality, Tanks and Filtration
What discus need to breed: warm soft clean water, tank setup, frequent water changes and gentle filtration.
Drum Filter vs Sump: Which Suits Your Aquarium?
Compare a drum filter and a sump for large aquariums and display tanks: solids removal, upkeep, space and when to use both.
Fish Quarantine System: Design and Protocol
Why a quarantine system protects your collection, how to build one and a simple protocol for new fish.
Freshwater Aquarium: Setup, Filtration and Water Care
Set up and run a freshwater aquarium: tank size, filtration, cycling, stocking and routine care.
Freshwater Stingray Aquarium: Tank Size and Filtration
What freshwater stingrays need: large tanks, sand, warm clean water and strong filtration for heavy waste.
Saltwater Aquarium: Protein Skimmers, Filtration and Stability
How to run a saltwater aquarium: salinity, protein skimmers, biological filtration, live rock and tank stability.
Water Quality for Fish: Ammonia, Nitrite, pH and Oxygen
The key water quality parameters for fish systems, safe ranges, how to test them and how to fix problems.
Drum Filter Mesh Size: How to Choose the Right Micron Screen
How to choose a drum filter mesh size in microns for ponds, RAS, hatcheries and aquariums, and the trade-offs of finer and coarser screens.
Drum Filter Troubleshooting: Causes and Fixes
Fix common rotary drum filter problems: constant backwashing, overflowing, torn screen, noisy drive and poor solids removal.
Rotary Drum Filter (RDF): How It Works and Where to Use It
What a rotary drum filter is, how screen, backwash and sludge removal work, and where RDFs are used in ponds, RAS and aquariums.
Biological Filters: Nitrification, Media and Sizing
How biofilters work: nitrification, media types, oxygen, sizing from feed load and common failures.
Moving Bed Biofilters (MBBR): Design and Operation
How moving bed biofilters work, how to fill and aerate them, and where they are best used.
Trickle Filters: Biological Filtration and Degassing in One
What trickling filters are, how they treat water and strip carbon dioxide, and where they suit best.
UV System for Ponds, Aquariums and Aquaculture
How UV-C sterilisers work, what they control, how to size one by flow and contact time, and how to maintain the lamp.
Ozone System for Aquaculture and Aquariums: How It Works and Safety
What an ozone generator does in water treatment, contact time, safety, and when to choose ozone over UV.
Water Circulation Pumps: How to Choose for Ponds and Aquaculture
How to choose a circulation pump by flow, head, efficiency and reliability for ponds, RAS and aquariums.
Gravity-Fed or Pump-Fed Filters: Which Is Better?
Compare gravity-fed and pump-fed filter designs for ponds and aquaculture: solids handling, energy, layout and reliability.
Turnover Rate: How to Calculate It for Ponds, Tanks and RAS
What turnover rate is, the formula, typical design values for koi ponds, aquariums and fish farms, and how it sets pump and filter size.
Turnover Rate by System Type: Ponds, Aquariums, RAS and Natural Pools
A comparison of typical turnover times for koi ponds, display aquariums, RAS tanks, hatcheries and natural swimming ponds.
Sump and Pump Station Design: Where the Clean Water Goes
How to design the sump or pump station after a gravity-fed filter: volume, level control and pump protection.
Turnover Rate and Biofilter Contact Time: Faster Is Not Always Better
How flow rate affects biofilter contact time, why pushing more water through can lower treatment, and how to balance flow.
Gravity-Feed Pipework Design: Slopes, Levels and Air Locks
How to design gravity-fed pipework for filters: pipe size, fall, avoiding air locks and keeping solids moving.
The Aquarium Nitrogen Cycle: A Plain Guide for New Keepers
What the nitrogen cycle is, how to cycle a new aquarium and what to do when ammonia or nitrite appears.
Aquarium Water Changes and Maintenance: How Often and How Much
A practical routine for aquarium water changes, filter cleaning and testing, with tips for freshwater and saltwater.
Hydroponic Pump and Reservoir Sizing: Flow, Volume and Run Times
How to size the pump and nutrient reservoir for a hydroponic system, including flow per channel, reservoir volume and timers.
Hydroponic Algae Control: Light, Nutrients and UV
Why algae grows in hydroponic systems and how to control it with light exclusion, clean water and UV treatment.
NFT vs Deep Water Culture vs Drip: Which Hydroponic System to Choose
Compare the main hydroponic systems on crops, cost, risk and filtration needs to choose the right one.
Hydroponic Water Temperature and Oxygen: Keep Roots Healthy
Why warm nutrient solution causes root rot, what temperature to aim for and how to cool and aerate hydroponic reservoirs.
Aquaponics Cycling and Start-Up: The First Six Weeks
How to cycle a new aquaponics system, add fish and plants in the right order, and what to test as bacteria establish.
Aquaponics Problems and Fixes: Yellow Leaves, Low pH and Sick Fish
A troubleshooting guide for common aquaponics problems: yellowing plants, falling pH, algae, clogging and fish stress.
Feed Conversion Ratio and Waste Load: Why Feed Sets Your Filter Size
How FCR links feed to growth and waste, and why daily feed is the best starting point for sizing filters and oxygen supply.
Biofloc vs RAS vs Earthen Pond: Which System for Your Farm?
Compare biofloc, recirculating systems and earthen ponds on water use, control, skill, power and risk to choose the right fit.
RAS Power Backup and Alarms: Planning for the Day Everything Stops
How to plan generators, oxygen backup and alarms so a power cut or pump failure does not kill your stock.
Koi Pond Aeration: How Much Air Do Your Fish Need?
Why koi ponds need extra aeration, how to size an air pump and diffusers, and when summer heat makes it essential.
Swimming Pond Plants and the Regeneration Zone
How plants and gravel beds in the regeneration zone clean a swimming pond, which plants to use and how big the zone should be.
Nitrification Explained: The Bacteria Behind Every Biofilter
A plain-language look at nitrification: the two bacterial steps, what they need to work and what slows them down.
Biofilter Media Types: Plastic Carriers, Sand, Ceramic and Brushes
Compare common biofilter media: moving bed carriers, fixed plastic, sand, ceramic rings and brushes, with pros and cons of each.
How to Size a Biofilter: TAN Load, Media and Reactor Volume
Work out biofilter size from daily feed, ammonia production and media conversion rate, with a worked example for trickling and moving bed filters.
Biofilter Start-Up and Cycling: How 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.
Carbon Dioxide in RAS: The Silent Stress and How to Strip It
Why CO2 builds up in recirculating systems, what levels cause stress, and how aeration, degassing and trickle filters remove it.
Nitrate Control: Water Exchange, Plants and Denitrification
Nitrate is the end of the nitrogen cycle but it still builds up. Learn how to keep it down with water exchange, plants or denitrification.
Dissolved Oxygen in Fish Systems: Targets, Drops and Fixes
How much dissolved oxygen fish need, why levels fall at night and in heat, and how aeration and oxygen cones keep them up.
Alkalinity and pH in Recirculating Systems: Keeping the Buffer Up
Why nitrification eats alkalinity, how pH drifts down in RAS and biofilters, and how to dose buffer safely.
Ammonia Toxicity and pH: Why the Same Reading Can Be Safe or Deadly
Total ammonia and toxic ammonia are not the same. See how pH and temperature change the danger, and what to do about it.
Pump Head Loss and Pipe Sizing: Why Your Flow Is Lower Than Expected
How pipe length, bends, valves and filters reduce flow, and how to size pipework so your pump delivers what you planned.
Airlift vs Pump Circulation: Moving Water Cheaply and Gently
Compare airlift pumps with electric water pumps for circulation: energy use, gentleness, aeration benefit and where each works best.
Ozone and ORP Control: Dosing Without Guesswork
How ORP (redox) monitoring is used to control ozone in aquaria and aquaculture, and why you should never dose ozone blind.
Ozone Safety: Destruct Units, Ventilation and Residual Ozone
Safe handling of ozone: why destruct units matter, how to ventilate, and how to stop residual ozone reaching fish and people.
UV Lamp Sizing and Dose: How to Pick the Right UV Unit
How to size a UV unit from flow, volume and the job it must do, plus how lamp ageing, water clarity and temperature change the result.
UV in Aquaculture and Hatcheries: Biosecurity at the Inlet and in the Loop
Where to place UV in a hatchery or recirculating farm, what it controls, and what it cannot do.
Drum Filter Installation Checklist: Levels, Drains and Power
A checklist for installing a drum filter: inlet and outlet levels, drain slope, power, wash water and commissioning.
UV Clarifier vs UV Sterilizer: Is There a Real Difference?
A UV clarifier and a UV sterilizer are the same hardware. The difference is the dose. Learn how to tell which you need.
Drum Filter Maintenance Schedule: Daily to Yearly
A practical drum filter maintenance schedule: what to check daily, weekly, monthly and yearly, and which spares to keep.
How to Size a Drum Filter: Flow, Solids Load and Mesh
Work out the right drum filter size from your flow rate, daily feed, mesh choice and installation space, with a short worked example.
Drum Filter Wash Water and Sludge: What Happens to the Waste?
Every drum filter makes sludge. Learn how much wash water it uses, where the sludge goes, and how to treat or reuse it.
Drum Filter vs Disc Filter: Which Suits Your Farm?
Drum filters and disc filters both screen solids out of recirculating water. Here is how they differ and how to choose between them.
Short answers
Questions we get a lot
How fast should the water go round?
For a koi pond, once every hour or two is the usual target. Fish farms and recirculating systems run faster than that. The turnover article has a calculator if you want an actual number.
Which mesh should I pick for a drum filter?
Somewhere between 40 and 100 microns covers most ponds and farms. Going finer gives you clearer water but you will pay for it in backwash cycles.
How long before a new biofilter works?
Plan on about a month and a half, a bit less in warm water. Keep testing ammonia and nitrite and do not stock fully until both stay at zero.
When does a UV lamp need replacing?
Roughly once a year if it runs all day. A lamp can still look bright long after it has stopped doing its job.
Still stuck?
Tell us about your setup
Write a few lines about what you keep or grow, how much water you have and what is going wrong. One of our engineers will read it and reply with a suggestion.