I’ve got some extra space in that fuge, so I have an Idea. I like the idea of having an anoxic (ie anaerobic) zone for denitrification. This is the old idea of a big deep sand bed (like, 6″ deep). But they have a crippling downside...there’s usually some nasty sulfuric stuff in there we don’t want to EVER get loose in the tank because it can cause some nasty catastrophes. So, some people have opted for a remote DSB where you run the water over the top of this R-DSB, letting the sand soak up the nutrients and the anaerobic bugs to do their thing, but can close a couple ball valves and it is no longer ‘touching’ the system. The idea being that while you get the benefits of a DSB, you can take it offline cleanly to clean it out occassionally, and you don’t have some sand-sifting animal that mistakenly stirs up the wrong part of the sandbed.
The idea is that there are bacteria which, in the total absence of oxygen, will rob an oxygen off of nitrate (enzymatically binding that oxygen to a carbon to supply the sugar the bacteria needs). That effectively converts the nitrate (NO3) into nitrous oxide (NO2), or even molecular nitrogen (N2), which are gasses and will (probably invisibly) bubble out of the water. This entirely removes the nitrogen of the system. Presumably, this (as well as uptake by things like algae) is how nature manages nitrates in the ocean.
So here’s the idea; I think I’d use two that I do maintenance on in opposite cycles.
Build it:
Materials: a bucket and sand to fill it up.
Get a regular HDPE bucket and remove the metal handle (or get one with a plastic handle)
Fill it up with sand, maybe 1″ below the rim. I’m going to suggest a sand no smaller than 0.5 mm, but no huge grain either. Smaller grain holds the oxygen out a little better, but larger grain will be easier to clean.
drop it in the fuge (remember: I’m planning on having a huge stock tank as the fuge, so there’s lots of space in there) and forget about it
6-12 months later, do it again so you have two in there. This isn’t really necessary, but I’ll have the room and I think it will aid in stability because I’ll clean them alternately.
Maintain it:
Materials: about 50lbs of clean sand (assuming 5g buckets are used) a large PVC pipe, hammer, wood block, smaller pvc pipe and plug/cap that fits in the large PVC pipe (barely).
Timing is debatable, I’m thinking 1 year is a good starting point, but I’ll see how it goes, I’m hoping to wait long enough there are a few nasty sulfuric zones in there. But I don’t want to wait so long the whole thing is super nasty.
get a PVC or ABS pipe approximately 1/4 to 1/2 the diameter of the bucket (you want large enough to get a substantial core, but small enough it’s not a huge fraction of the sand in the bucket) and a big hammer, probably a block of wood. The pipe should be taller than the bucket, maybe by a few inches.
Remove the bucket from the fuge, gently pour (’decant’) the water off the top as you take it out. This can be into the fuge, there’s no risk regarding the water sitting on the top. Note you’ll need new saltwater to add to the tank while the bucket is out for a few days.
Set the bucket on something very stable, that provides good support on the bucket’s bottom.
Pick a spot (probably the middle) and push the PVC pipe straight down into the sand with your hands as far as you can, this just makes the next part a little more stable.
Holding the wood block on top of the pipe, hammer on the block to drive the PVC all the way down to the bottom of the bucket. You might pre-check heights so you know it got all the way down.
Leaving the pipe in place for now, scoop out the rest of the sand. As the pipe gets loose, you can remove it, but be careful to make sure all the sand stays in the pipe as a core. I suggest leaving it until you can get to its bottom and use a thing piece of plastic to hold the sand in the bottom while you lift it out. You want a nice clean core that’s not disturbed at all.
You can throw out the old sand, or you can probably clean it. I’m going to try using a couple 200 micron socks and a garden hose, or I might try a pillow case idea I heard about. Just make sure you’re cleaning is thorough, then leave it out to dry for next time.
Lay the pipe at an angle in the bucket so the bottom is on one side and top of the pipe is leaning out the other side of the bucket. This makes sure the old core of sand (populated with the anaerobic bacteria you have not disturbed and exposed to oxygen) are spread out across the bucket. Don’t worry if a little spills out the bottom of the pipe, as long as most of the sand in the core is undisturbed and you leave anything that comes out at the bottom (don’t mix into new sand), it’ll be fine.
Start pouring in new clean sand. I debate the next step. Do you need to remove the large PVC a few inches at a time, or can you wait until it’s full and do it all at once? I’d prefer the latter, but I’m unsure of how much force that might take.
Ideally, fill up the whole bucket with your new clean sand, and slowly add some saltwater (tank water is probably best) until the water stops seeping into the sand. I suggest stopping the sand 0.5-1″ below where you want it to be later.
Then leave it all sitting still for 1-2 days WITH the PVC pipe still in place, you can just leave it on the garage floor, it won’t matter to the bacteria in the core. The idea is to give the bucket time to become anoxic, mostly this will happen on its own. if you want, you could speed up the process by using live sand, or seeding the new sand with a little from your system. But just leaving it alone for a few hours may be enough, I’ll probably do a few days.
Then put the smaller PVC pipe with plug/cap into the big PVC pipe, then (this might be hard) keep the small pipe in place and pull the large pipe straight out of the bucket (at the angle it’s laying at). The idea is to pull that shell off around the core, leaving the core in place, then cover with the last 0.5-1″ of sand, especially covering the cavity that will be left where the pipe came out.
Once the sand is settled in the bucket, slowly lower the bucket into the fuge. Slowly to minimize disturbance to the sand. And remove the excess water (that you added when you took the bucket out)
Fuggetaboutit
The idea is that the core of sand you left will be the seed for the new sand, and it stayed anoxic the whole time so that bacteria is still ready to keep working. You’ve removed a lot of detritus from the bucket that’s been building up in the bucket’s sand, since you probably pulled at least 4g of sand. Plus you’ve removed a good portion of any nasty zones in that DSB. I think having two buckets is best, so one is about halfway through its maintenance cycle (and has hard-working bacteria) when the other one just got refreshed.
I suspect you could clean one bucket per year or even every other year with two buckets running, most people that reported substantial problems with DSB toxicity didn’t run into that until 4+ years in, and that was when the sand was disturbed in the tank water, which won’t happen here. So, filling two buckets might cost $50 on the first bucket, and $50 on the second bucket a year later. Then about $50/yr to replace the sand if you toss/replace the sand; I plan to try to clean my sand and put it back, making this free except the tap water used for cleaning.
I plan to initially do a bucket every year (so the bucket is in for two years before cleaning), but hope to extend that to a bucket every other year (bucket is in for four years) if all is going well.
Note: you can do this smaller. you could use little paint mixing pails (the all-plastic ones), there’s really only a few rules if you want to follow my idea:
It must fit at least 6″ of sand depth. if it’s less than 6″, you won’t get much anoxic zone as the top inch or two still has a fair amount of oxygen.
It should probably be 4-6″ wide or more. It doesn’t actually matter because the bucket wall is solid and won’t let oxygen in. The important part is to be able to get a core to preserve for seeding the new sand. in a 4″ pail, you can probably use a 1″ PVC pipe and be ok, though pushing the sand out of the 1″ pipe will be pretty tough.
Fits somewhere in your setup, preferably two of these fit. This is probably mostly a footprint issue, but it must be short enough that wherever it is, the rim is underwater. You could probably run the bucket somewhere else, letting a little water from a manifold run over the bucket surface and taking the overflow off the top somehow, but that seems like too much work.
You might want it dark, it certainly doesn’t need light. a little algae growing on the surface won’t hurt anything, might actually help with nutrient export if you pluck the algae off occasionally (without disturbing the sand).
If two don’t fit, you’re probably fine...just know that it may lack some stability since the whole solution is brand new instead of 50%. Make extra sure to keep the situation anoxic while refreshing the bucket, and you’ll still keep it going.
If you’re really needing a custom thing, you could build your own ‘bucket’ out of acrylic or something, actually having a clear panel would be fun to watch. Just be sure to seal it well so the whole depth is anoxic, and make sure it’s short enough to have water exposure on the top. Oh, and don’t do a divided reservoir like dosing containers; you need to take one out at a time while the other stays put.
You’ve got your tank… so what do you put in it ? We have covered water quality and rocks but what about substrate ?
Let’s have a quick run though.
We have two options when thinking about the bottom of your tank.
Sand bed
To be honest sand beds are my favourite. Not only do they look more natural but they also give you bio diversity to your tank. Every grain of sand will overtime become full of…
A common fear among casual freshwater aquarists when it comes to the use of sand substrates is the dreaded anaerobic bacteria that reside in the substrate. So the tale goes, when the substrate is disturbed it releases bacteria or other substances that quickly kill the aquarium inhabitants. But is this myth true?
Overview
The Deep Sand Bed (DSB) is a term that describes a thick layer of sand (or similarly substrate with fine particle size) in aquariums that harbors different types of bacteria that work together to change some types of nitrogen into others. Much like the beneficial bacteria that accumulate in filters, these focus on changing harmful ammonia into something less toxic to fish. There are different types of bacteria in these sand beds, based on how much oxygen they are subjected to:
Aerobic - Bacteria that operates properly when exposed to significant levels of free oxygen (not bonded to other elements)
Anaerobic - Bacteria that requires very low levels of free oxygen
Anoxic - Bacteria that only tolerates oxygen when bonded (for example, as CO2, carbon dioxide)
The depth of the tank plays a big role here. A DSB needs at least 3 or 4 inches of substrate to harbor the three categories of bacteria listed above. Smaller sand beds will likely not have an anoxic region and those with only around an inch or so may not have an anaerobic region.
Based on posts around the internet, it’s normally the anaerobic bacteria which get the bad reputation for accumulating gases which have the potential to kill the fishes in your tank. Is this true, however? The answer, perhaps surprisingly, is both yes and no.
Functions of the DSB
So what exactly does the DSB do in an aquarium? While there is the transfer of nutrients from layer to layer that is useful for rooted plants, the two main functions to be explored here is nitrification and the reduction of sulfides. A simplified chart showing these processes is included below.
Nitrification
The process of nitrification begins with ammonia from the water column (as a result of aquatic animal respiration) and from the organic layer of waste products on top of the sand (commonly referred to as mulm). Within the aerobic layer, the bacteria here convert the ammonia to nitrites and then to nitrates. Some of these nitrates are utilized during the sulfide reduction process (more on this below), but the rest is converted to a harmless nitrogen gas in the anaerobic layer. From here, the nitrogen bubbles to the surface of the sand layer, through the water column, and upon reaching the surface of the water, oxidizes and goes away. This is actually the completion of the nitrogen cycle, whereas the beneficial bacteria in filters only do part of the entire cycle. This is why we do water changes: to remove the nitrates that would otherwise be unable to leave the system.
Sulfide Reduction
Organic waste in the sand, including proteins, eventually makes its way to the anoxic layer of the substrate where it decays into a combination of hydrogen sulfide and carbon dioxide. Bacteria in the aerobic and anaerobic layers convert this hydrogen sulfide (H2S) into sulfate components (with a little help from nitrates in these layers). Some sulfates are released into the water column, others stay in the sand either to be utilized by plants or to travel back into the anoxic layer.
Disrupting the DSB
Anaerobic and anoxic bacteria are an essential part of this type of system, commonly utilized in marine and pond systems, but also viable in freshwater. Being oxygen-sensitive, these bacteria can only work as intended if the sand is not significantly disturbed (smaller burrowing creatures and plant roots do not tend to be that intrusive). However, when the DSB is in upheaval, this bacteria is sent into the water column, which results in two things: a delay or stopping of denitrification and iron/sulfate reduction processes and the production of H2S from incomplete anaerobic decay.
In theory, H2S is toxic to fishes and can harm them. This is typically what the theories against DSBs focus on. In practice, H2S oxidizes quickly and generally does not harm fish in the small period of time it actually exists in the water column. It really only has the potential to become a problem when the entire system is disturbed at once, which may use up enough oxygen to stress fish (especially those who are oxygen-sensitive like Tinfoil Barbs and Iridescent Sharks). This can easily be avoided by removing fish prior to major removal of the substrate of the tank. That said, I have personally had no issues regarding the removal of the substrate (about 1/3 of the tank’s gravel at a time in a 55 gallon tank) with fish like Zebra Danios still in the system, but I do understock which may help in that regard.
An Aside on Anaerobic Bacteria
It’s interesting to think about how much concern the presence of anaerobic bacteria causes to some freshwater aquarists. Marine aquarists, on the other hand, have been using DSBs in their systems for years (with fishes that are much more sensitive than those found in freshwater, even) with remarkably few issues. In addition, live rock contains anaerobic and anoxic areas as well, which is what allows them to be the effective biological filters they are known for. That some people actually pay for this bacteria because of its usefulness should help put things in perspective.
Summary
There are several significant benefits to having a DSB in your tank. Mainly, it helps cut down on nitrates in the system and provides a means for nutrients to make their way from the top of the system down to the layers where plant roots are. There are also remarkably few downsides in practice. Bottom line, DSBs are worth considering in any system where you have the space to do so.
Baru beli rumput chaeto untuk filter biologi di aquariumku. Sementara aku taruh di atas live rock agar kena sinar matahari. Nantinya aku taruh rumput chaeto ini di sump agar sekalian membentuk refugium di sump aku. Pertanyaannya, itu sump sudah ada sistem deep sand bed (DSB) dan juga live rock, ditambah chaeto bisa membentuk refugium ngga ya?
