Biofilm
Up-Close and Personal!
This revealing discussion was posted on the Nishikigoi International magazine's web board. (See Links page) James P. Reilly, aka "JR" or "James P", gets up-close and personal with what we call "beneficial bacteria." Just knowing they are *there* isn't enough for JR! Where he gets to it, there'll be a link for some graphs and a picture he also posted on the NI web board.

This was posted in response to a question on "turnover rates."

Posted by James P on 5/28/2002, 2:33 pm , in reply to "The old rule was....."

The "old rule" will win out in the end as the best overall flow for an OUTDOOR closed system. The reasons are numerous. There are indeed a group of considerations that are satisfied with the once every two hour rule:

1) The movement of water slower than the old rule will not have the proper gas exchange or mixing of layers.

2) The old rule will work with the typical number of drains/pipe size and filter sizes we use.

3) If stepped up flow is attempted,the operation of four to six pumps and two air blowers(To move once every 20 minutes) will run around $300 a month in some areas of the U.S. This makes the hobby unaffordable for most in the hobby.

4) Koi need areas of rest, away from currents. They are not marine fish that constantly swim in fast moving waters.

5) Microbiologists have shown that biofilm subjected to water flow force are eroded and changed by water shear. The structure of active biofilm is programmed genetically but the environmental impact provides for ideal or disruptive conditions.If rapid flow is coupled with abrasive forces, such as sand and plastic rubbing together, the rate of detachment is increased. This can be a good thing or a bad thing based on the species growing within the biofilm.

So we have practical,economical,physiological and functional reasons for recommending the old rule. You can flirt with slightly faster (once every hour or once every three hours and do fine.Once every two hour is an ideal and reflects a consideration for and understanding of the koi, the biofilm and the reality of economics.There are many examples of bad koi keeping environments that are aided by faster moving water.There are also inferior filters that are aided by slower moving water.But after all is said and done, these recommendations are usually a compensation for something being done incorrectly to begin with-- overstocking, bad biofilter design, over feeding, limited surface area, poor mechanical filtration etc.The ultimate obstruction to moving the total water volume say once every 15 minutes is the macro detritus.This is a problem on two levels. 1) physical blocking or constant suspension 2) the added difficultly of creating a dominate species biofilm in the presence of maco detritus.

Just my humble thoughts on the subject.

JR

**** The Thread Continues ***

Posted by James P on 5/28/2002, 5:13 pm , in reply to "Re: The old rule was....."

Hi (name deleted), first I'm not trying to be purposely vague here but this is a huge topic. When I was referring to the old rule, I was purposely covering the broadest range of considerations.It is true that flow for current considerations alone can be isolated and be quite different from the filter turnover conversation. This is one reason why I like the old rule even though there may be some compromise in any one of the individual considerations.

I had asked Michael or Roland to consider the challenge of turning over a pond once every 15 minutes ( through filters). 7,000 gallons total volume is a turnover of 28,000 gallons an hour. I know you know the math- how many drains needed? How many pumps? How large are the vortexes? Nitratechs? Seems quite challenging and the bacteria won't know the difference since there will be the same number of nitrifiers as when you were circulating 7,000 gallons.two points:

* The bacteria's conversion of ammonia is instantaneous upon contact.

* The instantaneous conversion is an on going process.

The nitrifying population is in a state of equilibrium with the biomass. Like being "more dead" or "more pregnant" the ambient ammonia level is a "condition or state". Yes,ammonia must be delivered to the biofilm but the final ambient ammonia reading in a mature pond is constant low ( undectable) range. The target is to keep ammonia as an undetectable ion and so much "white noise" in the environment.

Here's a really stupid picture illustration for your consideration.

A backhoe is digging a hole. A row of men with wheelbarrows is wheeling it behind a wall and coming out the other side with empty wheelbarrows.Over time, the wheelbarrows are operating continuously and the backhoe is filling the barrows as quick as the the digging can be done.To keep the line moving,the backhoe takes shallower and smaller loads to fill each wheelbarrow as they pass.Soon the height of fill in each barrow decreases to a small amount.Add another backhoe and this breaks down.Remove every other wheelbarrow and this system breaks down.Please note the line doesn't stop due to workers throwing dirt OVER the walls!That would cause the dirt to build up on the wrong side of the wall!Now add another thousand men with wheel barrows, each moving CONTINUOUSLY. You have some men with empty wheelbarrows heading behind the wall. There can be only so much dirt delivered by t

(It was at this point that JR lost his train of thought, his mind, or both! And the post ended abruptly.)

*** After a brief nap, (or something, I suppose) Mr. Reilly picked it up, again. ***

Posted by James P on 5/28/2002, 9:57 pm , in reply to "Re: The old rule was....."

I knew I was asking for it when I came up with that dumb analogy! Usually I make my NI posts with one hand on the six shooter! Let my guard down on this one! Let's forget about backhoes and wheelbarrows!

(He NEVER DID finish this analogy! I was really getting into it!)

Ammonia isn't eaten by bacteria the way a dog chews a bone( OK , that's the end of my analogies, promise!) it is an instantaneous reaction. The koi put out the ammonia in an amount determined by body mass/diet and temperature.The bacteria grows to a level that can be sustained by that output. This is called equilibrium.If the ammonia is delivered to the filter on a constant basis, the ammonia leaving the gills is constantly diluted by the returning water and then once again this water is delivered to the biofilter.The net effect is a non detectable level in the ambient ammonia.The definition of ambient ammonia being " the level of ammonia that exists on all sides or put another way,encompassing the environment.Because this is a constant process and because ammonia is free flowing from the koi,the rate of production is equal to the rate of oxidation.

Gotta go and move the wheelbarrow, see ya, JR

*** Later that day, I think, someone noticed that JR used the word, "undectectable." Of course, this prompted further discussion! ***

Posted by James P on 5/30/2002, 5:48 pm , in reply to "But..."

(Name deleted), nitrite should NEVER be detectable in a mature pond. So when we are talking about nitrite readings there can only be one of two explanations. Either the pond is going through new pond syndrome and the filter is immature or the filter has never properly matured and the second phase of nitrification is being effected by too much ammonia being produced, anaerobic activity within the biofilm (denitrification = nitrate converted to nitrite). Chemical use and over cleaning of a BB can be other causes.This is a long subject that needs to be fleshed out in a few posts. Maybe we can revisit it as a separate subject at some point.

JR

*** Somewhere in all this, a nit got picked and JR broke out the BIG words! ***

Posted by James P on 5/30/2002, 9:47 pm

(Name deleted) brought up a very interesting topic regarding nitrite presence.I suggested that nitite should never be measurable in a healthy,mature pond. So why do so many folks pick up trace readings and spikes in their pond water ?( I will call this bulk liquid for this discussion).

The causes can be numerous but settle around two basic events.

1) The pond is going through an initial cycle and this unsettled period ( often called new pond syndrome)is characterized by an unreliable conversion of toxins by the newly established biofilter.

2) The environment available for bacteria favors other species or produces too much ammonia or lacks an important element to allow for stable bacteria populations.

First,a few comments about nitrifiers.

Although we think of ammonia oxidizers and nitrite oxidizers as "team mates", in truth,their interaction is at best, one of commensalism and maybe more precisely, one of protocooperation( meaning beneficial in a commensal relationship but both can exist quite nicely alone). The reason we have both types in our biofilters, is due to the fact that we create an ideal environment to favor certain dominate species to settle in.But the substrate and general environment can vary and many other species will also settle in. Many can oxidize ammonia just as well as the ones we desire. The key is the mixure of ammonia,nitrite and oxygen and detritus. Even ammonia oxidizers can be killed by too much ammonia. Most wild biofilms will be the home to a few dominate species and many others in competition, mutualism, commensalism, amensalism and parasitism with surrounding neighbors.

So out of this chaos comes form and order.The nitrite oxidizers will usually establish first in a wild pond environment. But if the ammonia level is very high( usual in the normal closed system), the growth of this population will be retarded and occur as a second dominate population.This is the result of two factors. 1) the ammonia oxidizers will be very prolific and tend to crowd out the budding nitrite oxidizers and 2) the nitrite oxidizers tend to stop reproducing in the presence of high ammonia.

I mentioned two situations that cause ammonia spikes.I think the second reason is more common that koi keepers realize. Many keepers will test the ammonia and nitrites in a new pond and track the rise and fall of ammonia. But it is probably more helpful to follow the rise and fall of nitrites to truly understand the new pond period.

If waste is allowed to accumulate in the biofilter, you will get a quick start up but you may be plagued by nitrite spikes for months. why? The likelihood is that a mixed biofilm of heterotrophic bacteria are still dominating the system (in normal situations this is just a phase and we evolve past it in the new pond syndrome period) and cleaning of detritus (their favorite growing surface) reduces their numbers. Secondly,small over crowded ponds tend to experience ammonia surges that knock down the nitrite oxidizers periodically. There are many variations of this dynamics based on temperature, biofilter design and DOC content of individual ponds. And correcting short comings of these conditions can shift the mix within the lush multispecies biofilm. This is running long so I'll finish.

JR

*** One of the participants in this discussion thought perhaps he had managed to get on JR's nerves. Now, that *can* be done, but you *really* have to work at it! ***

Posted by James P on 5/31/2002, 1:41 pm , in reply to "Re: nitrite should never be detectable"

(Name deleted), no I don't get irritated even if I pretend to! I find it great fun to turn on the "light bulb" in fellow keepers minds the way it was turned on for me when I got deeper into this subject. I have some great photos from some research done on multispecies biofilm that really help to visualize what these films look like. I'll try and post some this weekend. I think you have the chemistry exactly correct but you may have missed the physical reaction and biofilm design realities. Biofilm is a relatively thick,porous layer of polysaccharides that is both elastic and confining. WITHIN the biofilm matrix are the bacteria cells. The bulk liquid outside this matrix is different than the fluid inside in terms of substrate available for oxidation. This is one of the reasons that we need to deliver the ammonia filled water to the surface of the biofilm matrix along with saturated oxygen levels. Because the matrix is expandable and a porous membrane,fluids enter and oxidation of ammonia is spontaneous. The interior fluid and the outside bulk liquid will eventually be in equilibrium due to this oxidation. Within the matrix, nitrite oxidizers are acting on nitrite as it is produced internally. If the levels rise beyond the populations ability to oxidize them, the excess passes out of the biofilm membrane and back into the bulk liquid environment.

The pond water itself favors floating heterotropic bacteria forms. They are also acting on ammonia( especially in the form of feces) and DOCs. This is the dynamics that can take over in dirty overstocked ponds. BUT then again, a properly designed,properly filtered and properly stocked pond shouldn't have this level of "fuel" to begin with. And a fine mechanical filter like the Answer causes the water column to be less favorable to heterotropic species and more friendly towards aerobic nitrifiers. And Don't get me started on BBs!

JR

*** Click HERE and a new window will open with some charts and the photograph JR mentioned. ***

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