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A O U
  S w e d e's     D o c k

Anaerobic Bacteria
&
Lava Rock
On the Ponder's Bible email list a "discussion" periodically pops up regarding Anaerobic Bacteria and the use of Lava Rock as filter media.

In a likely vain attempt to enlighten ponders I will go into a little more detail about each and how they relate to each other.

The word anaerobic means "absence of oxygen" (at least as far as this discussion goes). That's all it means. It isn't poisonous nor is it inherently toxic. You could breathe in anaerobic air and not be killed (as long as you quickly replaced it with aerobic - oxygenated - air). You probably wouldn't feel too good for awhile but you wouldn't be dead. So in that sense, anaerobic conditions (AC) aren't toxic, as opposed to breathing in nerve gas or something like that which would kill/damage you regardless of how much nontoxic air you got afterwards.

That said, nothing can live in anaerobic conditions for very long (well some stuff can, but I'll get to that next). Fish, for example, will die quickly (in minutes) if left in anaerobic water. Effectively they will suffocate, just as we would if we couldn't get oxygen to our lungs.

Under anaerobic conditions (AC), toxic bacteria can develop over time. For example, Botulism, an extremely toxic poison, is one that can form. There are (numerous) others, though few as deadly as botulism. However they are not created instantaneously. It (they) takes weeks or even months to develop (though some forms of botulism can form in days), just as it takes weeks/months for the beneficial ("algae eating") bacteria to get established in an aerobic pond.

Even in the unlikely event if something as deadly as botulism does form, it will quickly "die" (lose effectiveness) when exposed to oxygen, much as aerobic organisms will die if subjected to anaerobic conditions. It would have to be ingested by fish pretty quickly to harm them.

Anaerobic Conditions come about when organic material decays (oxidizing) and "burns up" the available oxygen in that section of water and is not replaced or replenished. This cannot occur in moving water. (Well it can but not as far as we ponders are concerned. If the pond were sealed by a sheet of plastic (or ice) for example.) As water is exposed to the air, the oxygen in the water is very quickly replenished.

There is much discussion about the use of lava rock (or even gravel) as a filter medium and how it can harbor toxic Anaerobic Bacteria. While technically true, this is misleading (to be generous) and patently false (to be accurate) under conditions reasonable for ponds.

There are spurious claims that lava rock harbors pockets of Aanaerobic Conditions & Anaerobic Bacteria, and as such is inherently dangerous to use in an upflow filter. While it is possible, it is as likely to occur in a reasonably maintained filter (flushed/cleaned periodically, even if less than optimally, in normal circumstances) as your chances of walking on the moon (some folks have, but not very often).

If the filter is allowed to stay clogged up (inadequately or even unflushed) for long periods (causing channeling) then anaerobic pockets are likely to develop in those sections that are stagnant. Just as they would in ANY other media or filter where there was no circulation. It would take a pretty long time for toxics to develop and it's my contention that anyone who neglected his pond for that long can't blame anyone or anything other than himself and to do so is petty rationalization. ("It's not my fault Judge, I had an impoverished childhood!")

Even in that (extreme) case, almost by definition the anaerobic water can't reach the pond. It's trapped (created) only in nonmoving water within sections of the filter.

There are claims that lava rock get "plugged up" internally and creates poisons. That's a clear fallacy on at least three fronts:


         
  1. It defies the laws of physics.

      In order for material to penetrate the rock solidly enough to plug the passages, there has to be greater pressure on the outside than the inside. If there was anywhere near enough pressure to do that, the water would simply just flow around the rock. Unless of course the filter discharge of the media were allowed to become so plugged all the pressure of the pump was on the rock. Even then it is extremely unlikely.

      Presuming it did happen (excess external pressure), when the pressure was relieved (lowered), the internal pressure created by forcing stuff into the passages would blow it back out. This, of course, is a pretty unlikely scenario as well.

      Taking it a (ridiculous) step further, if passages did get plugged, it almost certainly would be with organic material that would eventually decay and unplug naturally.


         
  2. That bacteria grows so much on the internal surfaces of the rock to such an extent they eventually plug the passages in the rock.


      This is absolutely absurd. The bacteria require a surface to adhere to. If, in fact, they could grow upon (adhere to) each other, they would eventually plug ANY passageway, no matter the type of media. That would include the Mighty Mississippi over the last several million/billion years of accumulation. All rivers would be a miles wide and an inch deep. Think about it.


         
  3. Let's presume (for argument's sake and against all logic) that:


      (a) Anaerobic Conditions did occur in a pond (or its filters) - As has been shown (with only unusual and extraordinary exceptions), Anaerobic Conditions will only exist in small out of circulation pockets. For it to damage anything outside the area it has already damaged, either the animal (life form) has to move into the affected area or the affected area has to move to it.

      In the former case what fish (or any living mobile creature for that matter) would move into, or stay in, an environment that would harm it? Life preserving reflexes alone, if not conscious effort, would quickly repel it. (How long would you willingly stay in a smoky room where it was hard to breath?)

      In the latter case, the act of moving will cause the "bad water" to mix with aerated water, thereby neutralizing/eliminating any lethal potential it may have. Presume a cubic inch of Anaerobic Conditions, with a zero oxygen level, water moving into "healthy" water. As it moves, that action alone will cause it to effectively disperse and mix with surrounding water, say only another cubic inch, that is aerated at probably somewhere near, if not exceeding, 10ppm. The combined level of the 2 combined cubic inches is now 5ppm, at or above the level needed to support fish. AND this presumes a "1 bad to 1 good" mixture, when in all likelihood, if such a scenario where to occur at all, the ratio of exchange would surely be 1 bad to 100's (if not 100,000's) of good. (For comparison, a single gallon of water is over 200 cubic inches.) In which case, the total oxygen content of the water would be essentially unaffected (perhaps infinitesimally reduced by .01 ppm or something on that order).

      To bring an entire pond to an anaerobic condition would require an extraordinary condition. Like leaving the pump off for several days in very hot sunny weather. Even then it would be unlikely unless the surface were sealed. (Note it is entirely possible that without adequate circulation for pond oxygen levels to get so low as to cause larger fish to suffocate, if the population is higher than the pond would normally support without external aeration. Which most ponds are.)

      (b) harmful Anaerobic Bacteria did develop. - As has been shown, it can exist only in Anaerobic Conditions. Exposure to oxygen effectively kills it (though there are exceptions). If, in fact, it did exist inside the lava rock, it can't harm anything because by definition there can't be any movement of water through the rock, otherwise the AB couldn't develop in the first place. If there is no movement of water, it won't get out of the rock to harm pond life, at least not in harmful quantities. It would ooze out very slowly at best where it would be immediately nuetralized.

      So for Anaerobic Bacteria to harm pond life, it has to be ingested pretty quickly for it to do damage. Can it happen? Sure. It is likely to happen in a filter or pond? All but impossible, or as likely as you dying from ingesting moon dust.

      Again, and again, and again,
      a healthy pond requires circulation and aeration (and there even exceptions to that "rule"). One is almost synonomous with the other. All that I've tried to do here is dispel some of the ignorant, even malicious (however well meaning), anaerobic myths that periodically pop up around pond circles.

      As far as filter media go, in the final analysis, the name of the game is surface area supporting bacteria, which in turn 1) use up nutrients before water discoloring algae can get to them and 2) break down harmful fish wastes (ammonia in particular) before they can build to toxic levels.

      Whether lava rock is used for filter media, or plastic jujubes, is really immaterial. All that counts is that it do the job. I like lava rock because it is relatively cheap, gives a big bang for the buck in terms of surface area, does not break down or wear out. And it can provide quite a bit of detritus removal as well, depending on the grit.

      Further I believe the water does not flow per se but is effectively drawn through the rock by the "respiration" of the bacteria (for lack of a better term). Bacteria operate on the molecular level (which is pretty small) and I believe "ingest" and "expel" water at that level throughout the interior of the lava rock.


    In any case, even if that isn't true and there is no "work" done internally in the lava rock. The external surface is great enough to get the job done.

    I have used (much of) the same rock in an upflow filter design for over 10 years (in several different housings before my current and hopefully last stainless one). My pond stays crystal clear and my fish and plants are healthy (as long as I don't do something stupid that is {grin}).

    The people who use lava rock must number in the 10's, if not 100's, of 1,000's in the world. I have personal knowledge (people who have written me) of 100's who have used it building upflow filters according to the design I have in my book - Ponders Bible. . And there is certainly at least a magnitude more who have built filters using the same design, either from the book or the website. Of all those people, less than 10 have ever complained to me about it not working over the years. That's a 99%+ satisfaction (or at least not complaining) ratio. Pretty darn good I think.

    End of Anaerobic Bacteria


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