Background & Theory:
The system of nitrate and phosphate reducing bio pellets represents the latest evolution of carbon dosing and is therefore sometimes referred to as solid-form carbon dosing. Aquariums employing carbon dosing have also been referred to as bacteria-driven systems, in that they rely on bacteria (bacterio-plankton) to reduce the inevitable end products of the nitrogen cycle and other metabolically produced nutrients... nitrates and phosphates!
Carbon dosing is based on the following:
"¢ All living things (perhaps excepting that bacteria recently found growing in arsenic) require four foundational nutrients in order to survive and thrive... to build their DNA structures. These nutrients are Oxygen (O); Phosphorus (P); Nitrogen (N); and Carbon (C);
"¢ These nutrients are utilized in fixed ratios specific to the subject life-form; for example, it has been referenced in this thread (by TMZ; Post No. 3066) that phytoplankton utilizes 106C:16N:1P; Oxygen was not referenced, but I would assume that it is utilized in a greater proportion than Carbon;
"¢ So in effect, what carbon dosing does is supply the C... and as would be expected from any properly functioning biological filtration system, bacteria will develop based on the availability of other required nutrients, namely N, taken from Nitrate (NO3); and P, taken from Phosphate (PO4). These along with Oxygen are available within your water column;
"¢ As bacteria assimilate all of these nutrients required for their growth, from the aquarium; formerly inaccessible nutrients (namely nitrates/phosphates) now become accessible as both skimmers, and activated carbon are very good at pulling organic compounds from the water column;
In the end, the function of a bacterial-driven filtration system can be summarized in this way: The aquarist provides an organic food source (ethanol; vinegar; sugar; and now bio-pellets); bacteria use nitrate; phosphate; and oxygen available in the water column to complete their basic requirements for growth; nitrates and phosphates are suddenly bound into an organic form that protein skimmers (and activated carbon) can grab a hold of; finally the protein skimmer pulls out copious amounts of bacterial mass which has captured N & P, thereby reducing nitrate levels and phosphate levels in the aquarium bulk water. The above is the basic principle for all forms of carbon dosing, not just biopellet filtration systems.
Liquid form carbon dosing involves supplying the carbon food source to the entire water column. As a result, organic carbon is available to the entire system - display tank and filters. The perceived drawback of which is that bacteria and other life forms are encouraged to develop throughout the aquarium system, and many believe liquid form carbon dosing can pose a higher risk of unsightly cyanobacteria, and other such blooms taking hold within their display.
In theory, the introduction of bio pellets (i.e. solid-form carbon dosing) adds increased control to the prior art of liquid/supplement based carbon dosing by confining the Carbon food source to an isolated area of the aquarium system, as opposed to distributing it throughout the entire water column.
Quick Reference:
"¢ Biopellets are actually biodegradable polymers "“ PLASTICS. The more common types of plastics are PHA "“ Polyhydroxyalkanoates and PCL "“ Polycaprolactone, however different manufacturers/suppliers are introducing their own biodegradable plastic formulas;
"¢ Most recent brands of biopellets are comprised of a smaller unit size. This like most other bio-dependent strategies is based on the understanding that the smaller the media in a given space, the larger the surface area available for bacteria;
"¢ Biopellets are best employed in fluidized reactors. Most media reactors can be retrofitted; however the success of the pellet system is reliant on evenly fluidized movement. If there are dead-spots in a reactor, or flow biased areas, the pellets will inevitably clump together in the areas of insufficient flow. Once the pellets begin to clump/stick to each other with bio-film, they will either float on-mass to the top of the reactor (clogging the outlet), or begin to smell unpleasant (anaerobically derived H2S).
"¢ Rather than having to keep an eye out for clumping; and consequently shaking up the media every few days, it is best to find a well fluidizing reactor. To this end, there are a number of new reactor designs reaching the market which employ conical bases; and more importantly, function without the use of sponges, which have been found to trap bacterial mulm rather than allowing it out of the reactor for removal (skimming) from the system water;
"¢ Flow of water through a biopellet reactor is a balance between maximizing media contact time, while eliminating the risk of clumping due to insufficient flow... i.e. if the reactor fluidizes beautifully, you can run just enough system water through to allow the pellets to fluidize evenly and thoroughly; if the reactor flow is uneven, your focus should be to ensure the weakest flow areas don't clump.
"¢ Most distributors will recommend an ideal volume of pellets per total aquarium volume; however it has been found that one should always start slowly (approx. ½ the recommended volume), especially when introducing the pellet system to an old or established tank. Over the course of a few weeks to a month, the amount of pellets can be gradually increased to the recommended running volume;
"¢ Because the pellets are a food source, and as such, will be consumed over time, one should expect to replace a quantity of digested pellets every few months or so depending on the rate of consumption;
"¢ The effluent from the pellet reactor should be directed as close to the skimmer intake as possible, but is best routed directly into the skimmer intake [100%]. This allows the skimmer first access to pulling out nitrate and phosphate laden bacteria before it gets a chance to circulate throughout the greater aquarium system. Inevitably, some of the bacteria will make it through the skimmer, and in theory, should become a bacterio-plankton food source for corals and other micro-fauna; and
"¢ .... it is normal course for the aquarium to become cloudy with a bacterial bloom upon initialization of the biopellet system. The bloom should run its course within a few days of operation. It has been reported that in those systems which do not employ a skimmer, the blooms will continue to reoccur.
Caveats:
Some cautionary notes are offered, but not limited, to the following:
"¢ Dropping nitrates and phosphates too abruptly will adversely affect corals, hence the strong recommendation to start with ½ the distributor recommended quantity;
"¢ The larger the bacteria population the greater the reductive effect on pH. Should you require a large volume of pellets, you must also have very strong oxygenation strategies in place: i.e. over-sized protein skimmer; rapid water movement; use of ozone in an under-sized skimmer; etc;
"¢ Keeping in mind that the four nutrients most heavily involved in this type of bio-filtration are Carbon; Nitrogen; Phosphorus; and OXYGEN, consideration of the last should be part and parcel of the implementation of this strategy. Otherwise, one will experience difficulty maintaining pH above 7.8 - 7.9 when large quantities of pellets are employed; which will have a detrimental effect on sps and lps corals, as they will have trouble gaining and retaining calcium required for their growth; and
"¢ The function of the entire system is limited by the availability of any of the required nutrients. That is: if there is no P "“ the reduction of N is stalled; if there is no N "“ the reduction of P is stalled; and if there is no C the reduction of both N and P will cease. As a result of this knowledge, as well as the normal course of phosphates being continually introduced with feeding and related activities, it is highly recommended that one continue to employ GFO or other phosphate reduction strategies even after nitrates successfully settle at 0ppm.
The above represents a high level summary of some of the thoughts and discussions surrounding the use of this relatively new bio-filtration strategy. The list is by no means complete as hobbyists continue to discover new refinements to the best usage practices advertised and established for the employment of bio-pellets. But if I were to give a short guideline for using this system, here it is:
1. Get a good fluidizing reactor;
2. Start with ½ the volume of pellets and ramp up over the course of the first month;
3. Route the pellet effluent through a good strong skimmer;
4. Super-saturate your system with oxygen in order to avoid the reductive effects of respirating micro-fauna;
5. Monitor the health of your livestock very closely throughout the implementation of any new husbandry practice!!
