Understanding Bio-Pellets
By Guy Walker
By Guy Walker
In this article I will cover the basics of bio-pellets in a way the average person can easily understand. All of the information within is not only derived from research studies and published articles, but also from my own personal experience with over 20 years of practical knowledge in the hobby.
What are bio-pellets?
Bio-pellets are bio degradable polymers used as a solid carbon source for carbon dosing. There have been many forms of carbon dosing, including vodka, Glucose (table sugar), and vinegar, but with the advent of bio-pellets (biodegradable polymers) carbon dosing has become a much easier and more stable form of nutrient export.
What is carbon dosing and how does it work?
Bacterial growth in reef aquaria is carbon source limited.
What does this mean?
This means the amount of bacteria in the aquarium is limited to the available carbon if the carbon is low, in turn the bacterial count will be low as well.
Adding a digestible carbon source therefore, will spur bacteria population growth and with that growth, other necessary nutrients like nitrogen and phosphorus-containing compounds will be scavenged from the water column.
Mechanical filtration via protein skimming will remove bacteria from the aquarium water column and with them their nutrient load.
What does this mean?
This means that the excess bacteria in the water column after taking up Nitrate and Phosphate will then be removed by the protein skimmer removing these nutrients from the water column permanently.
Rapid bacterial growth via the digestible carbon source will constantly replenish the bacteria being removed by the skimmer. Without the skimmer Bacterial populations can become much too high and an unhealthy bloom can take place. For this reason, it is very important to have a good protein skimmer.
How do we run bio-pellets on our system?
We run bio-pellets in an up flow media reactor with the outflow directed in to the skimmer compartment or directly in to the skimmer itself.
Why do we use an up flow reactor?
We use an up flow reactor to cause the pellets to tumble. This is done for two reason; One is to help keep the chamber clean of detritus and waste material, but the main reason is the tumbling action helps to dislodge biofilm (bacteria) from the pellets and force them out of the reactor to be exported via the skimmer.
Why direct the outflow to the skimmer?
This is done to export a large amount of bacterioplankton, which are the excess bacteria coming off of the pellets, and also to remove excess carbon from the water exiting the reactor. Excess carbon in the main water column can also feed cyano bacteria, so it is important to try and keep as much of the carbon source as possible in the reaction chamber.
Bio-pellet reactors come in many different sized, shapes and styles
choosing the right one for your system is a mater of personal preference.
Center photo of DIY Reactor built for 600g system
choosing the right one for your system is a mater of personal preference.
Center photo of DIY Reactor built for 600g system
What are the dis-advantages of Bio-Pellets?
In some cases you can promote the growth of cyano bacteria because cyano bacteria can also use the carbon as a food source resulting in their growth even in very low nutrient aquariums. This can be avoided with the use of a good protein skimmer and proper reactor installation.
It has been shown that the use of bio-pellets can lower ALK and PH in the aquarium so monitoring these levels and possibly using counter measures may be needed. ALK and PH drops are due to lower Oxygen levels that can be caused by bio-pellets. I have found the use of an air injection system will help counter this issue. For me personally, it has solved the problem completely.
Bio-pellets can actually run your tank to clean for certain corals to thrive e.g.: Zoanthids and Chalices. I have heard of this problem many times from hobbyist and at one point even experienced it myself for a brief time. The way I combat this is really rather simple and works well in my systems. I significantly reduce the number of water changes I do on my systems. I also heavily stock my fish. This helps keep my tank from becoming to clean, so to speak. I also use calcium reactors which are known to release some nutrients back into the system, as well as trace elements and minerals.
What are the advantages of using Bio-Pellets for carbon dosing?
One of the advantages to bio-pellets is the use of a reactor for carbon dosing.
Not having to calculate and measure things like Vodka, Sugar Vinegar etc. for carbon dosing since the bacterial population will be self-limiting.
Not having to carbon dose daily.
A considerable advantage of using biopolymers in water denitrification is the reduced risk of contaminating the water with soluble biodegradable organic carbon.
Bio-pellets produce bacterioplankton. It is an excellent food source for many corals. Not all will get skimmed out and some will become coral food.
· The ability to reduce nitrates and phosphates to undetectable levels.
· The ability to raise your stocking limit or bio-load
· The ability to feed more resulting in healthier and happier livestock
· A significant decrease in algae growth
· Less tank maintenance
Wellsophyllia Brain Coral
Feeding from the water column
Do all bio-pellets work the same?
Bio-pellets are made up from only two base polymers, poly-3-hydro butyrate (P3HB) and 3-hydroxybutyrate-co-3-hydroxyvalerate (P3HBV), both of which are polyesters. A more stable decrease in phosphates has been reported with (P3HBV).
Why would one polymer work differently than the other?
These polymers are created by the biological metabolism of sugars or alcohols by bacteria. Basically, not only are these polymers food for bacteria but, were themselves created by bacteria.
Different species of bacteria are used in the production of these polymers and in turn different species of bacteria will feed on them. Different bacteria act differently when processing nitrogen and phosphorus containing compounds.
Different brands of bio-pellets have been shown to work differently than others
Why is this?
This can be attributed to which of the two base polymers are used.
Fillers added to the bio-pellets may also affect the way they work. The fillers added by different manufacturers are not all known. There are known fillers that increase the effectiveness of the pellets like ceramic powders to increase porosity giving more surface area for bacterial colonization.
When implementing any new or unfamiliar technology to reefkeeping, your best chance for long term success is to have a basic understanding of how that technology works. Solid carbon dosing has been the single best addition to my style of reefing and I urge any who are thinking of trying it out to do so. It may not be the answer for your reefing personality but then again it may be that one thing that takes you from being a successful hobbyist with a nice aquarium to a successful hobbyist with an amazing reef.
References
Bacterial Counts in Reef Aquarium Water: Baseline Values and Modulation by Carbon Dosing, Protein Skimming, and Granular Activated Carbon Filtration
Ken S. Feldman, Allison A. Place, Sanjay Joshi, Gary White
The essential role of hydrodynamic shear force in the formation of biofilm and granular sludge.
Liu Y, Toy JH.
Environmental Engineering Research Centre, School of Civil and Structural Engineering, Nanyang Technological University, Singapore, Singapore. [email protected]
Use of biopolymers as solid substrates for denitrification.
Rodrigues AL, Mosquera-Corral A, Machado AV, Moura I, Matos MI, Brito AG, Nogueira R.
Source IBB - Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho, Campus de Gualtar 4700-057 Braga, Portugal.
Co-immobilization of bacteria and biodegradable solid substrates in polymer matrices for denitrification of water
A, Heinemann, W.R. Muller University of Stuttgart.
Polyhydroxybutyrate: Plastic Made and Degraded by Microorganisms
Christine R. Hankermeyer, Ronald S. Tjeerdema
Inorganic Nutrients, Bacteria, and the Microbial Loop
D. A. Caron Microbial Ecology Vol. 28, No. 2, The Microbial Loop (Sep. - Oct., 1994), pp. 295-298
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