Surprising. Filter auto-cleaning by bacterial colony? - The Planted Tank Forum
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post #1 of 8 (permalink) Old 08-22-2019, 06:37 AM Thread Starter
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Surprising. Filter auto-cleaning by bacterial colony?

Hi

I want to comment here and ask you about what do you think is the explanation of something I experienced yesterday. I think it is very interesting. I have some theories but I am not sure.

I have a garden pond (3000l) and the filter is a pressure filter with 3 sponges, some filtering balls (Sera crystal clear) and about 7-8 litres of Sera Siporax (ceramic/crystal cylinders for biological filter).

During the last filter cleanings (for months) the Siporax, which is ceramic white when new, was always brownish (milk-chocolate color). I think this is normal. It was not possible to clean more, even killing everything using hydrogen peroxyde (which indeed improved the color but not so much).

Last time I cleaned the filter was 7-10 days ago, I think. Last saturday, I had to make some work in the pond and bypassed the filter. Quite a lot concrete dropped into the water and everything was covered by cement dust so I emptied the pond, cleaned it completely, etc. This took until tuesday afternoon, when the refill was over with 1/3 tap water + 2/3 RO water.

Yesterday afternoon I opened the filter to clean it. I was expecting -aside of dead bacteria- a roten egg smell, but when I opened it, I smelled what it was fishy odor (ammonia) mainly, maybe mixed with a very slight odor typical when water gets too much time closed (maybe a hint of anaerobic metabolism?). The sponges and filter balls where clean (sponges had a bit of dirt, normal as it has been in use 7-10 days only). But to my surprise ALL the ceramic cylinders (Siporax) were clean as new! Nice ceramic white!

I have not used bleach, hydrogen peroxyde, nor any conditioner in the pond water before puting it in bypass.

I did measure NH3/4, pH, and O2 of the remaining water inside the filter:

NH4= 10 mg/l
pH = 8.0
O2 = 4 mg/l (*)

(*) Please, note that this is measured on the remaining water inside the filter, this water has been agitated by me when removing by hand all the 7 litres of Siporax, so I guess I have oxygenated it more or less (I did not know I was going to find a cleaned Siporax, so I did not put care about not to agitate it so to test for O2 later...).

The water in the pond did not have 10mg/l of NH4, which with a pH of 8 (this is the average pH I have in the pond) would lead to NH3=0.53 mg/l which is deadly for fishes. My fishes were all fine.

Normally the pond is heavily aerated and O2 levels are close to saturation (near 8 mg/l now in summer).

During the previous week before putting the filter in bypass, I have been filtering with Al2O3 (alumina oxide) to remove PO4 and SiO2, I did not see any clear improvement in the pond (algae, etc).

The brown color that had the Siporax before these days could be:

a- Good bacteria colonies
b- DOM (organic matter) in the pores.
c- Algae

I discard 'a' because the gravel in the bottom of the pond did not develop never a brown color as the one in the Siporax (even in the bottom side of it, far from the light), so I don't think that the brown color is bacteria colony. Moreover when Siporax was new and the pond was cycled (for months, even one year and so), the siporax did not have that color! It was acquired slowly with the pass of years. About 'c' option, I doubt it because the filter is in complete and permanent blackout.

At this point I was thinking what could have been the cause of the cleaned Siporax. My hypothesis is: depletion of most O2 (maybe not all) during the four days the filter has been off, then heterotrophic (saprophytic) bacteria has developed and reduced all DOM (organic matter) in the Siporax converting it to NH4/3. But I still see some problems with this idea:

- If all O2 is depleted then the saprophytic bacteria should be anaerobic. If so, then why the odor was not rotten eggs mainly? Maybe it is there, but 'covered' by the fishy/ammonia smell?

- If O2 is heavily reduced but still there is some, maybe there was saprophytic aerobic bacteria...(they do exist) but I do not know if they could appear and being significant in aquarium/pond environment with low levels of O2.

- Even if the cause was a colony of heterotrophs reducing DOM, why it did not work like that in normal use of the filter (i.e. with oxygenated water flowing)? Why it did clean the DOM only when the filter was stopped? Maybe is it because heterotrophic (saprophytic) needed place to colonize and it was already took by the autotrophic NH3 reducing bacteria/archaea in the Siporax, so they needed to die first so to give the place to heterotrophs to settle? Or maybe is saprophytic anaerobic bacteria much more efficient than saprophytic aerobic bacteria? I don't know, but according to what I have read, it is just the opposite...

EDIT: I remember now that monday I opened the backwash connector at the top of the filter (it stayed opened for 1 day and a half or so) to work on the output pipe, I did not smell anything (I did no try, though), but maybe this could have vent some gasses...?

I would like to hear what do you think could have been the process here, or if you have had some similar experiences. I am still puzzled -although happy- by this.

Last edited by Darkbluesky; 08-22-2019 at 11:26 AM. Reason: Wording
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post #2 of 8 (permalink) Old 08-22-2019, 11:37 PM
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I believe that the brown crud we see on ceramics and other media is dissolved organic compounds (DOCS). It's the material that is left after decomposition. Typically the only way to restore soiled media is with a 50/50 bleach/water solution to burn off the organics. I don't know what happened in your pond to clean the media...perhaps a caustic from the cement dust?
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post #3 of 8 (permalink) Old 08-22-2019, 11:48 PM
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Agree. I think the abrupt pH raise could very well kill the "stain" of living organisms on your ceramic rings.

Nothing good happens fast in an ecosystem.
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post #4 of 8 (permalink) Old 08-23-2019, 12:11 AM
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Here's my guess. The crud was held on by living bacteria / slime. That layer of biofilm makes it hard sometimes to clean media. Bleaching it breaks the bonds and makes it easier to rinse the organics away when cleaning. In the filter, once all the bacteria died from lack of flow and oxygen. It released its grip from the media and easily washed away.
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post #5 of 8 (permalink) Old 08-23-2019, 02:21 AM
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I personally think it is a mineral deposit. If your pnd is a little short on chlorides and sulfate. micro nutrients typically are sulfate or chloride. If those nutrients run low some of the micros may be converted to oxides and plate out on the media. which may result in a black, brown, or yellow mineral coating. however if the chlorides and sulfates concentration may increase dropping your PH a little (maybe not enough for you to notice) and that may cause the mineral deposits to dissolve.

Bleach is often used to help remove mineral deposits. The minerals convert to chlorides which dissolve easily.
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post #6 of 8 (permalink) Old 08-23-2019, 06:44 AM Thread Starter
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Quote:
Originally Posted by Blue Ridge Reef View Post
Agree. I think the abrupt pH raise could very well kill the "stain" of living organisms on your ceramic rings.
Only that I think that the filter was in bypass when cement dropped into the water… (I could not swear it, but it is what I recall). Anyway if not, this could add to what both, Amp2020 and Surf say.

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Originally Posted by Amp2020 View Post
Here's my guess. The crud was held on by living bacteria / slime. That layer of biofilm makes it hard sometimes to clean media. Bleaching it breaks the bonds and makes it easier to rinse the organics away when cleaning. In the filter, once all the bacteria died from lack of flow and oxygen. It released its grip from the media and easily washed away.
When some time ago, I thought I had bacteria dead (filter 24h stopped, and I cleaned it with tap water -I knew I killed the bacteria that may have been still live-) I could not clean at all the crud, so I am not sure about this but maybe some time or/and biological action is needed before the bacteria looses and the organics could be removed/rinsed away. Even so, I suspect the crud might be 'protected' from scrubber or washing by the micro-cavities… On the other hand, is it so hard the biofilm, as to protect the crud from scrubbers? Maybe yes.

But on the other hand what you say could make sense theoretically, and in fact, it could be the explanation why this 'crud cleaning/removal' does not work when filter is running normally. I have been thinking and I suspect that maybe the driver has not been depleted O2, as the water was saturated with it, but the NH4/NH3/NO2 needed to feed the bacteria/archaea which was -as it should- much less present than O2 (non measurable) in pond water: I think that the NH3/NO2 was depleted long before the O2, good colony died, O2 remained, thus as you say, then the bacteria released its grip from the media, and saprophytic aerobic bacteria took over and reduced the DOM to NH4/3. This would explain why I had in the filter water, 10 mg/l of NH3, (when in pond water did not), and why there was no rotten egg smell present.

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Originally Posted by Surf View Post
I personally think it is a mineral deposit. If your pnd is a little short on chlorides and sulfate. micro nutrients typically are sulfate or chloride. If those nutrients run low some of the micros may be converted to oxides and plate out on the media. which may result in a black, brown, or yellow mineral coating. however if the chlorides and sulfates concentration may increase dropping your PH a little (maybe not enough for you to notice) and that may cause the mineral deposits to dissolve.

Bleach is often used to help remove mineral deposits. The minerals convert to chlorides which dissolve easily.
That is a smart one, I did not think on that, I will keep this in mind. Regarding our case I am not sure: I can't remember what I could do to increase these concentrations (maybe if the cement has them, and the filter was not in bypass -which I think it was). Nevertheless, this would not explain the big increase in NH4/NH3 in the isolated filter water… Except if the DOM needed to produce -biologically- NH4/NH3 would come from other parts of the filter and the crud disappeared as you say…. But if the DOM used to produce NH3/4 comes, for example from sponges (not the ceramic media) then why it (I mean, massive production of NH3/4 and sponge/other media cleaning) did not work all the time and not only when filter is stopped?

Besides, the sponges had the normal (few) dirt for a week of filtering when I opened the filter…

Do cement increase sulphates and chlorides?


I think I could do a test when the ceramic media gets dirty once more. I have added bottom aeration to the filter. It will be normally closed (only used for backwash). I guess next time, having water oxygen saturated I could bypass the filter, let it sit for four days or so with aeration, and check if the dirt is gone after this time.

Last edited by Darkbluesky; 08-23-2019 at 09:29 AM. Reason: Wording
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post #7 of 8 (permalink) Old 08-24-2019, 08:35 PM
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Quote:
Do cement increase sulphates and chlorides?
No but GH boosters do. Some just provide sulfates in the form of calcium sulfate and magnesium sulfate. Others use Calcium chloride and magnesium chloride. Since plants generally need more calcium and magnesium than sulfur and chlorine I typically see a lower PH in water with actively growing plants. Many micro fertilizers use sulfate and chloride ingredients although in much smaller quantities. And you can use potassium sulfate and potassium chloride in the macro fertilizer. But keep in mine that having excess potassium may increase PH and increase deposition of minerals.

It should be noted that mineral deposits can be created chemical means or biology may create them. Sometimes both chemical and biology are involved:

https://en.wikipedia.org/wiki/Desert_varnish

https://en.wikipedia.org/wiki/Stromatolite


https://pdfs.semanticscholar.org/382...568dbbc7ee.pdf
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post #8 of 8 (permalink) Old 08-29-2019, 06:25 AM Thread Starter
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Quote:
Originally Posted by Surf View Post
No but GH boosters do. Some just provide sulfates in the form of calcium sulfate and magnesium sulfate. Others use Calcium chloride and magnesium chloride. Since plants generally need more calcium and magnesium than sulfur and chlorine I typically see a lower PH in water with actively growing plants. Many micro fertilizers use sulfate and chloride ingredients although in much smaller quantities. And you can use potassium sulfate and potassium chloride in the macro fertilizer. But keep in mine that having excess potassium may increase PH and increase deposition of minerals.

It should be noted that mineral deposits can be created chemical means or biology may create them. Sometimes both chemical and biology are involved:

https://en.wikipedia.org/wiki/Desert_varnish

https://en.wikipedia.org/wiki/Stromatolite


https://pdfs.semanticscholar.org/382...568dbbc7ee.pdf
Tx for this info. Then I rule out for the moment this hypothesis, as I have not added any fertilizer (and my K was really low) or other substance, neither introduced rocks, and it did not rain neither. I can't remember any factor that might have introduced some chemical change in the water (as said, I think to recall I bypassed filter before cement dropped into water).

For the time being, I still stick with the biological explanation. I would like to be sure though why it did not work (did not clean it) in normal filter use. I can only think on the needed surface by the DOM reducing bacteria to colonize/settle or as Amp2020, a biofilm holding the organics. But I am not sure. I would like to hear more opinions on that.
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