Anarobic Bacteria

[Bob Campbell]

Vlad I get that you are busy with your own project and I hope it's going well, but I wonder if you or others can give me a little advise about now.

I recently added about 24" of pumice to the bottom of my 48" deep fish tank.  So far everything is wonderful.  I've even been adding Urea to the fish tank to bring up the Nitrate levels until the fish grow large enough to produce enough waste on their own.

I check the Ammonia and Nitrite levels at least twice a day in order to keep the process within safe limits for the fish.  So far no problems, and my Nitrate levels are about 20 ppm.  .Nitrite will occasionally get a tad high, but several hours later it's all good.

My concern is dead spots in the 24" thick media.  The input water is dispensed into a perforated pipe that runs the length of the tank under the media.   Bubbles come up in only two spots which indicates to me that I may have dead spots within the media. 

The fish love to dig holes in the pumice.  Sometimes they nearly hit bottom.  I'm glad they keep it turned and I rake it smooth every few days.

There is no foul smells of sulfur, or any other smells, and the fish are eating better than before, so it still seems like the experiment is working well.  But I wonder if there is anything else I should be looking for.  If there was any problem I'd like to catch it early.  Is there a any thing I can test the water for to give me an early heads up?

[Fishy McFisherson]

Funny, I've just spent the last few hours researching freshwater deep sand beds an pondering how they could be applied to an aquaponic system.

Great minds think alike I suppose, which is why we're all here 

I found this article, which is written with freshwater aquariums in mind, but I found to explain the concepts (to a noob like me) rather well. Without seeing more detail on the nature of water flow in your system, and my very basic knowledge of fostering anaerobic conditions, my first thought is that having the water plumbed to the bottom of the bed, and flowing up through the media, may provide too much oxygen for anaerobic bacteria to set up shop. The previously noted source and most other sources I found in my googlings, strongly state that disturbing the surface of the media should be avoided at all costs.

But again, I've only just scratched the surface on this stuff and would love to hear if I misunderstand what is going on so I don't inadvertently create a Hydrogen Sulfide factory.

[Bob Campbell]

Thanks that looks like a lot of good information, and it confirms my suspicion that I need to use my nose to be mindful of the smell of sulfur.

My intention behind pumping fresh water down below the surface was to create a fluid sand filter. It falls far short of being fluid, but it has achieved a very good bacteria bed.  

In the article you linked they say not to disturb the media.  The fish love to dig deep holes, so I guess that is just going to be part of the routine.  I have also been raking the media flat, and using water pressure through a 3/4" pipe to keep the media stirred up every few days.  That's a routine I don't think I can find time for any longer, but I was concerned about anaerobic dead spots and thought it might help.  I'm glad to hear it would not be so bad to the a few dead spots develop.

Fishy McFisherson said:

Funny, I've just spent the last few hours researching freshwater deep sand beds an pondering how they could be applied to an aquaponic system.

Great minds think alike I suppose, which is why we're all here 

I found this article, which is written with freshwater aquariums in mind, but I found to explain the concepts (to a noob like me) rather well. Without seeing more detail on the nature of water flow in your system, and my very basic knowledge of fostering anaerobic conditions, my first thought is that having the water plumbed to the bottom of the bed, and flowing up through the media, may provide too much oxygen for anaerobic bacteria to set up shop. The previously noted source and most other sources I found in my googlings, strongly state that disturbing the surface of the media should be avoided at all costs.

But again, I've only just scratched the surface on this stuff and would love to hear if I misunderstand what is going on so I don't inadvertently create a Hydrogen Sulfide factory.

[Jon Parr]

Great read, Fishy. Thanks

Bob, WHY did you add 24" of pumice to your fish tank? I get the fluidized bed concept, but not sure why you would want in the fish tank, or even need it in an ebb and flow AP situation? Are you pumping in FT water to the bottom of the bed, or returning GB water? Are you wanting to encourage anaerobic activity? I assume not, since you are pumping water in at depth. Fishy's link is for a very different purpose than what I think you are trying to achieve. A deep sand bed is designed to encourage anaerobic avtivity, and all the benefits it provides, such as making metal ions in plants usable forms (ferrous iron, and others), CO2 production (great for algae and aquatic plants, not so great for fish, aerobic bacteria, or veggies), removal of nitrates by creating atmospheric N (again not a benefit for AP, unless your planted area is insufficient), and production of organic acids (of great benefit to hard water victims like myself, and a PITA for soft water folk).

The only value in the fluidized bed I can see is if you have raft AP without a media section, and even then I would prefer a mineralization tank, or polisher tank, filled with bird netting and gammarus. Much easier to see what's happening, and service, and effective at both biofiltration and transforming mineral solids into soluble nutrients. If you want the benefits of anaerobic activity, then a deep sand bed is dandy, though I would place it after the FT and before (or even in) the raft or media. That way the acids and metal ions are immediately available to plants, and the fish won't be bothered by the hydrogen sulfide emmisions. Vlad, TC, and I have discussed what BYAP calls a RSG filter on another thread (long story, but a filter designed to harbor the anaerobic benefits by a Really Smart Guy). I have had intention of building my own rendition of this, so I'm glad you brought up the subject.

[Jon Parr]

Upon re-reading your post, I think you are just trying to boost biofilter capacity to boost nitrates. And since you are adding urea, it is not an issue that your present biofilter is unable to keep up with your fish load. Again I have to ask why? Is your planted area so vast that you have a nitrate def? If so, I think your better off adding extra food, or compost, to feed the biofilter rather than urea which only provides N. When using urea, you will also be subject to adding the other micros and macros to balance the plant needs, and then you may as well run hydroponics, and not have to worry about the fish.

I don't mean to be disrespectful at all, hope it didn't sound that way. I'm just trying to understand what your looking for to try and help, if I can.

[Bob Campbell]

@Jon Parr - Initially I came up with the idea to place the pumice in the fish tank because it was too deep and too dark.  Now I can see my fish again.   I liked the idea even better after reading about fluidized sand filters.  The pumice is very light, and I thought it would move with the water flowing up though it. I was actually afraid it would not even settle, and I ran tests to be sure it would.  In the end I was wrong.  The pumice has settled, and there is very little movement other than the fish building nests.  This may be enough to keep it stirred up.  The holes they dig everyday are at least a foot deep..

Until I added this large amount of pumice to the fish tank I had never seen Nitrate test above zero.  I felt my plants would fair better with higher Nitrates and in fact I believe they will, but it's difficult to make a good assessment of that since I have only a few plants in the system right now.  But duckweed is growing much better in the higher Nitrate solution.

What I am looking for is a better Nitrate production.  Currently my fish are not large enough to eat enough to make enough Nitrate.  With the extra bio filter capacity I have been able to create more Nitrate.   You are probably right about the nutrient balance.  I'm still feeding my outdoor system with urine and may have to begin drinking a lot more coffee in order to supply both systems.

The pumice has been in the fish tank for several weeks.  It's indoors so if it does begin to foul I will probably become aware if it quickly.   I was not sure if that is all I should be doing to gauge the health of my tank.  After reading the article Fishy provided I feel my nose alone will be enough to keep that in check. 

If I had added only 6 inches I would not be so concerned about anaerobic bacteria, but 24" may create problems so I'm still being very watchful, and I'm ready with a bug out plan to quickly evacuate the fish to a safe area if things go awry. But so far this has been a win win situation.  I have the Nitrates, I can see my fish again, they are eating better and seem to enjoy digging in the pumice.

[Jon Parr]

Ahh. Got it. Are your plants experiencing any boost in growth as a result of the nitrates?

[Bob Campbell]

It's too soon to tell.  When I added pumice I removed all the plants from the raft bed in order to make a temporary tank for the fish.  I've got some seeds started, and a little water cress which appears to be doing well.  The duck weed is really doing well though.  Before the duck weed just barely held it's own.  Now it's becoming thick.

Jon Parr said:

Ahh. Got it. Are your plants experiencing any boost in growth as a result of the nitrates?

[Fishy McFisherson]

Oh, I get it. Neat idea, pumice seems like it would be light enough for a fluidized bed filter (FBF). Most FBF installs I've seen have the water flowing to the bottom of a column or cone and use a much finer media (THIS is a decent example of what I am familiar with). I feel like your concept will serve its purpose, but is more like a reversed under gravel filter than a fluidized bed filter. Still, any water flowing through neutral media isn't a bad thing, and provides more surface area for beneficial bacteria. I like the concept because it provides substrate for the fish to play around in but prevents accumulation of waste in the media.

Earlier in the design phase of my system, I was planning on integrating a FBF after some type of solids seperator. My thought was to change the media type & reverse the flow on a sand type pool filter (free on craigslist all the time) to make a diy version of the super expensive commercially produced FBFs.

[Chris Carr]

@Fishy. Great article. The last I kept fish I used this technique and it works great. I learned it from a back ally ornamental fish breeder I stumbled across in SF near the tenderloin on google maps. Such a shady place to find a gem of a shop. Their English was very minimal but they were happy to share their knowledge and I recall their setups being quite fascinating to me and pretty spot on as to how this article describes. They bred mostly live breeders at some high stocking densities. They had a good 5+ inches of a black sand but I am not sure of the source. Lots of plants and only a small in tank pump and no bubbler as this article describes but my memory might be a bit cloudy. I've poisoned off a bunch of brain cells from then until now. I do remember them saying they never did water changes either. I didn't do them either but my stocking density was pretty low.

I ran a 20 gallon with this Whisper 10i style pump and the system thrived. Lots of babies and with all the plants, lots of places for them to hide. 

Now that I understand more what was going on with this system id totally do it again for an ornamental setup or breeder tanks if space or ascetics were a concern but as Jon points out, there are probably more efficient ways to implement a larger AP setup.

If growing a swamp crop was of interest, it would be cool to see how far one could optimize this to measure its filtering capacity and possibly integrate crawfish/prawns into. "Swamp spinach" or water spinach is a popular green in Vietnam would would do well in such a filter bed but they usually just eat the wild stuff. It goes like a noxious weed just about anywhere, including Canada unfortunately. Not as bad as kudzu but I believe in some places it requires a license to grow commercially. Personally I am not a fan of the fibrous stocks.