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Bio Load in Aquarium or Pond


By Carl Strohmeyer-PAMR 40+ years experience
Updated 3/20/19

The "Bio-Load" is essentially the amount of life existing in an aquarium, pond, etc. and its affect upon the nitrogen process that places demand upon the aquarium's filter system. This includes mechanical, chemical, and especially biological filtration.
Factors that affect this include waste, nutrients, dissolved organic particulates/compounds (DOC), bacteria, plankton, and more.
This applies to both Salt and Freshwater as well as ponds.
As well the "Bio Load" affects the bio system not associated with filters, which includes plants and nitrification/de-nitrification outside of the filters.

A lesser known aspect of the aquarium (or pond) bio load is its affect on the Aquarium Redox Balance, yet these two have major interconnections.
An example would be a Redox that moves up in down with large changes in ORP likely indicates an aquarium with too high a bio-load, often adding oxidative stress to the inhabitants thus shortening their lifespan and lowering disease resistance.
Further Reference: Aquarium Redox Reduction, Oxidation, Balance

Excess Aquarium Fish Food
This "bio-load" is made up of uneaten food, decomposing inhabitants, accumulated organics and waste produced by livestock, foods and plant matter in the aquarium tank/system.
Often this bio load goes unseen decomposing in filters, especially canister and large wet/dry sumps.
As well, this hidden bio-load may be under rocks and other decorations, especially live rock reefs in marine aquariums.

The picture to the left shows trapped decomposition from uneaten food and other organics. This adds to the bio load and can also affect the Redox Balance requiring abnormally high oxidation levels. (please click on the picture to enlarge for a better view)

Best Aquarium Sponge FilterWhat is also noteworthy, while additional filtration will help handle a higher bio-load in an aquarium or pond, it is a finite number.
What I mean is, one cannot have a 60 gallon aquarium with say a Fluidized Sand Bed Filter/Reactor and a quality Sponge Filter, both of which are excellent bio filters (if not the best depending upon whether you purchased patented AAP Hydro Sponge or cheap Chinese knock off) and then say if I double these filters I can double the amount of fish so long as I keep up with dissolved oxygen levels in the aquarium!!
It simply does NOT work this way, as while good filtration and filter redundancy is definitely a plus, there is a point where too high of a bio load is too high a bio load!

This analogy goes for marine reef aquariums as well and in fact I have both observed and had dealt with customers with Marine Reef Aquariums whereby they thought their double Protein Skimmers and copious amounts of live rock would allow them to keep a very crowded reef tank. In the end, even the smallest changes would bring sudden changes in Redox or nitrate levels or even ammonia levels!

Product Resources:
*Patented High Bio Capacity Aquarium Sponge Filters, from AAP
*High Bio Capacity Aquarium Fluidized Sand Bed Filters/Reactors


Over populated with fish aquarium
Water changes is probably the best way to TEMPORARILY deal with a bio load that is clearly past its capacity.
This water change can be a flow through method where-by clean, mineralized, de-chlorinated water is constantly being slowly changed out.
Further Reference: Aquarium Cleaning; Methods

The picture to the right is a feeder tank at a pet store. This is an example of an aquarium that is clearly over stock and past its bio-load capacity.

However before I seem to condemn this practice, as long as these criteria are met this can be done for the SHORT term:

These above methods will maintain a balanced Redox, meaning both oxidation and reduction, which results in the fish being healthy and less risk of disease introduction when moved or more likely fed to other fish.

I should point out that part of my reason for even posting and explaining this picture of "Feeder Fish" is simply to show how extreme we can get in bio load and where one should NEVER be with the maintenance of our PET fish.

As well this is meant to demonstrate what we can do if only temporary to deal with a high bio load.
And finally to point out that many fish/pet stores do NOT follow many or even any of the practices I note here to deal with this hopefully temporary extreme bio load condition.

Another aspect of aquarium bio load is plants.
Plants certainly make for a more natural freshwater aquarium and in many ways are a better way to control many aspect of the nitrogen level since plants due not produce the nitric acid that nitrifying bacteria produce. Especially during daylight hours of photosynthesis plant increase oxygen.

However plants themselves can die and leave decomposing debris that adds to the waste aspect of an aquariums bio load.
As well during night when photosyntheis ceases, the plants will compete with fish for oxygen, so this is a consideration with a planted aquarium and its bio load.
With ponds, this becomes even a bigger issue as many outside plants that provide no benefit other than maybe shade can drop copious amounts of debris into a pond thus adding to decomposition.

An aquarium keeper should attempt to trim off as many dying or old plant leaves, and remove dead plant material from the bottom of an aquarium or pond.
If your tank has an algae problem, in particular a free floating algae problem, or if algae has been scraped off rocks, etc. into the water column, it is advisable to perform a water change and change/clean at least some filter media after such a scraping or use of a new UV Sterilizer to clear such an aquarium.

Overall, as with a filter, a well maintained heavily planted aquarium can increase the bio load capacity of an aquarium, but similar to additional filtrations, this is not a large increase.
This also applies to a Marine Reef Aquarium Refugium, whereby these definitely aid in nitrate control (& generally are an asset to any marine aquarium), but these also can add to bio load in other ways, especially if poorly maintained.

A few water parameters to watch as an indicator of a "too high" bio load are:

Finally, here is a ranking of filters that have from highest to lower in bio load capacity.
Please note that while this is an objective list based on ounce per ounce of bio capacity, it does NOT take into account different sizes of these filters or in the case of canister filters or wet/dry sump filters the type of filter media used (although I do break this up as best as possible).

Here is an excellent article that addresses in much more depth the advantages of the above mentioned filters (especially the differences in HOB filters):
Aquarium Filtration; Filter Review

Other Recommended Reference & Product Sites

Aquarium UV Sterilization
Aquarium or Pond UV Sterilization

Algone Water Clarifier & Nitrate Remover

An awesome USA made product; Nitrate fixating microorganisms incorporate excess nitrogen into the cellular mass, while bioactive enzymes assimilate nitrogen from the water column

Redox Test Meter

EcoSense ORP 15 Redox Meter

ORP Range -1200 to +1200 mV
Great for testing Redox before and after water changes, use of water conditioners, after addition of UV Sterilizer, etc.

*Aquarium Redox Balance

Aquarium Chemistry
Aquarium Chemistry

Wonder Shells, Only at American Aquarium Products
Wonder Shells, Regular & Medicated

Unique Version sold ONLY at American Aquarium Products.
Excellent for disease prevention!!!

*Aquarium Nitrate Control

Freshwater Aquarium Care
Freshwater Aquarium Care

Aquarium Lighting
Aquarium Lighting

Marine Aquarium Care
Saltwater Aquarium Care

Pond Care
Pond Care

TMC V2 RO Filter systems; the very best you can buy with TDS meter (far superior to 4 stage RO/DI systems sold via Bulk Reef Supply, Amazon, or eBay that use the inferior cellulose triacetate membrane made by Dow):
Reverse Osmosis Aquarium Water Filter, TDSReverse Osmosis Aquarium Water Filters; with TDS Meter


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In Chronological order of writing with the newest at the top

  1. How to Treat Sick Fish
  2. Whirling Disease in Fish
  3. Reef Aquarium Chemistry Maintenance
  4. Use of RO, DI, Softwater in Aquariums
  5. Lighting Theory of a Planted Aquarium- RQE, PFY, PAS, & PUR
  6. Aquarium or Pond Bio Load
  7. Tuberculosis in Fish
  8. PUR vs PAR in Aquarium Lighting
  9. Head Pressure in Aquarium and Pond Water Pumps
  10. Fin/Tail Rot For Betta & ALL Fish
  11. Angelfish Virus/Aids
  12. Activated Carbon
  13. Fish Baths/Dips as an aid to treatment
  14. Streptococcus gram positive bacterium in aquariums, Eye Infections
  15. Hydrogen Sulfide
    production in anaerobic De-Nitrification for Aquarium/Ponds
  16. Fish Shipping
  17. Aquarium Size, Fish Stunting
  18. Aquarium Algae,
    BBA & Brown Algae in particular
  19. Aquarium Salt (Sodium chloride) in Freshwater Aquariums
  20. Betta Habitat; Wild Bettas to Domestic Betta environment parameters
  21. HITH; Hole in the Head Disease
  22. Aquarium Protein Skimmers, Ozonizers
  23. Power Head/ Water Pump Review
  24. Molly Disease/ Mollies in an Aquarium
  25. Basic Fish Anatomy, Fin Identification
  26. Aquarium Moving/ Power Failures
  27. Octopus as Aquarium Pets
  28. Aquarium Nitrates
  29. Ichthyophonus protists, fungus in fish
  30. Aquarium and Pond Filter Media
    Types; Mechanical, Bio, Chemical
  31. Aquarium Water Conditioners (also Pond)
  32. Fish Parasites; Trematodes & Monogeneans; Annelids and Nematodes;
    Flukes, internal worms, Detritus Worms (often confused with Planaria), Micro Worms
  33. Aquarium Silicone Application;
    DIY Aquarium Repair & Glass thickness
  34. Pond Veggie Filters; DIY Bog Filter
  35. The difference between Plaster of Paris and Aquarium Products such a Wonder Shells:
    Identification, prevention & Treatment
  37. AQUARIUM TEST KITS; Use & Importance
  38. SEXING FISH; Basics
  39. Chocolate Chip, Knobby and Fromia Starfish
  40. Freshwater Velvet & Costia
  41. Usnic Acid as a Fish Remedy
  42. Aquarium Heaters; Types, information
  43. The Lateral Line in Fish, Lateral Line Disease
    or Head and Lateral Line Erosion (HLLE)
  44. Tap Water use in Aquarium; Chloramines, Chlorine
  45. Can Black Ghost Knife fish give an electric shock?
  46. Bio Wheel Review; Do Bio-Wheels really work?
  47. How do Fish Drink?
    Use of RO Water
  48. Cyclops, and Predatory Damselfly larvae
  49. Betta with Dropsy;
    Treatment and Prevention of DROPSY in all fish
  50. pH and KH problems in African Cichlid Aquarium
  51. Aquarium Gravel, which size?
  52. Blue green algae, Cyanobacteria in Ponds/Aquariums

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*Sponge Filters that far outperform all other brands or DIY:
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UV Replacement Bulbs/Lamps Directory:
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*A CLEAR POND; Care & Information

Fish Food Information:

Aquarium & Pond UV Sterilizer Use Articles
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Directions/ Instructions/Downloads; Aquarium Pond Products

Aqua UV versus TMC UV Sterilizer
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A comparison of the two top large pond/aquarium-system UV Sterilizers and why the AAP/TMC comes out as the best when price and dwell time is considered

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