Freshwater Deep Sand Bed (DSB)

[Anoxia]

OK, here's a new pic of my fresh-smelling aquarium, to show its progress. I trimmed back the hygro on the right already, it grows insanely fast. I have three plants I now suspect of being terrestrial bog plants rather than fully aquatic, but as long as they are willing to hang on, I will leave them in. I kind of hate the bubbler, but whatever.

Jungly, isn't it. Sorry I cropped the ends of the tank off. I added some more leaf litter just before the shot, so the leaves are still bunched up in a big wad, but they will settle.

I know valisneria is not a foreground plant, but I didn't know it was val when I planted it, because it was very small. I just bought a ton of plants all at once from the petstore, without finding out what they were called.

You can see a dark layer on top of the dsb. There is a bit of gravel on the surface, and that's what causes it. It reminds me of lasagna. I've noticed that the clay/potting soil "mud" layer in the middle isn't as prone to turning dark as the sand is, but I don't know why, or what that means. I'd love to find out.

 

[DeeDeeK]

You can see a dark layer on top of the dsb. There is a bit of gravel on the surface, and that's what causes it. It reminds me of lasagna. I've noticed that the clay/potting soil "mud" layer in the middle isn't as prone to turning dark as the sand is, but I don't know why, or what that means. I'd love to find out.

MMMMMMM! I'd eat a slice of that lasagna! :drool: (just kidding)

 

[Anoxia]

I finally found some decent praecox (neon dwarf) rainbowfish, but unfortunately they are all males. My cories are all males, too, and so are my black platies. Out of the 20 aquatic animals I'm keeping, only 3 of them are girls! It always puts this Flight Of The Conchords song in my head: http://www.youtube.com/watch?v=n5aY0CAtvsk

I think the mulm from the old gravel I left in the bottom layer, combined with the lack of surface agitation, is what caused the low oxygen problem in my aquarium, and therefore the neccessity of the dreadful air bubbler. I keep trying to turn the stupid thing off, but a few hours later my fish start breathing heavily, and I have no choice but to plug it back in. You live and you learn.

 

[DeeDeeK]

I'm so sick right now so forgive my choppy reply re. O2 levels and buried mulm. My thought is it's CO2 surplus, a much commoner problem than O2 deficit in tanks with any circulation.

Water is funny! It becomes oxygenated very easily, quickly, such that O2 shortages are rare so long as the surface is being mixed into the circulation of the tank and allowing less oxygenated water contact with the air. No agitation is needed.

Water holds lots of CO2 but doesn't exchange it as readily with the air as it does oxygen so it easily builds to levels out of equilibrium with atmospheric CO2. Agitating the surface releases the CO2 quickly enough to restore equilibrium in short order.

The symptoms of O2 shortage and CO2 surplus both are fish gasping at the surface.

The mulm you buried was at the bottom level so I bet it's either anaerobic or anoxic, so very very little or no oxygen is even reaching it - the upper reaches are already eating it all up. However, decay produces CO2 from all kinds of things even in the absence of oxygen, so that mulm may well be releasing lots of CO2, which will diffuse right up and out of the sand bed.

Bubblers are known not to boost O2 levels, except by causing the surface layer to roll over and be replaced by deeper water which, if you have a filter or powerhead oriented to disrupt the surface even gently is already happening. BUT, as I said before, agitation will release the CO2 and bubblers agitate the surface quite a bit.

OK, my bed is calling me. I hope I made some sense! The flu is a hell of a disease, my friends.

 

[Anoxia]

You made total sense! Thanks for explaining it to me. I hope you feel better soon.

Too much CO2 isn't that bad, a lot of people run expensive equipment to achieve high CO2 levels. All I have to run is an airstone. Looking at it that way, it doesn't seem like such a bad problem to have. Low oxygen would have been worse.

 

[DeeDeeK]

You made total sense! Thanks for explaining it to me. I hope you feel better soon.

Too much CO2 isn't that bad, a lot of people run expensive equipment to achieve high CO2 levels. All I have to run is an airstone. Looking at it that way, it doesn't seem like such a bad problem to have. Low oxygen would have been worse.

Oh, I think I must have misstated myself about CO2 and airstones/bubblers. The effects of a stream of bubbles rising to the surface are to a) bring water from the bottom to the surface of the tank, where it can absorb O2 (water equilibrates its O2 level with the atmosphere rapidly) and b) agitates the water at the surface which actually drives off CO2, up to the point where the water's CO2 content is balanced with the CO2 content of the atmosphere. Water for some reason does not exchange CO2 with the air nearly as readily as it does O2.

Here is a link, maybe a little hard to comprehend but it tells the tale of agitation and CO2.

I keep meaning to buy a CO2 test kit to see the difference between water in a non-DSB type tank or container, in equilibrium with the air, and the water in my DSB tanks, which can sometimes develop too much CO2, I believe since the water is circulating to the surface to take up O2 but not churning it and blowing off CO2. I've been challenged on the notion that freshwater DSBs can produce enough CO2 to enhance plant growth.

The fact that fish will gasp despite what should be more than adequate oxygenation is good evidence that the CO2 levels are elevated, most likely by the DSB and its decaying contents. The very frequent eruptions of gas bubbles from the DSB in my "big" tank - and they're not H2S (can tell because they don't stink) and probably not CH4, H2, N2, or N2O because of the frequency and volume - which are likely CO2 tells me that sufficient CO2 is being generated to enhance plant growth, although its release in the form of large bubbles rather than diffusing into the water column renders it ineffective.

It also tells me that the rate of diffusion of CO2 through the regions of the bed where its being generated is slow enough that the bed is becoming locally saturated, which is why the CO2 is coming out of solution and becoming a gas. Is enough CO2 diffusing out of the bed and into the water column to effectively enhance plant growth? I can't tell without a test kit. It could be too little or it could be that CO2 is just being generated quickly enough to keep areas saturated despite having adequate diffusion out to boost plant growth.

If diffusion is slow enough, dissolved gasses of all sorts will reach saturation and come out of solution. How slow the diffusion must be depends on the rate at which the gas in question is being generated. For example, one might have a tight substrate that's deep enough to accumulate H2S to saturation and develop bubbles. The substrate will resist the passage of gas bubbles due to being compacted and dense until the bubble is massive enough to lift the substrate above it and break through, drawing a bunch of sand mixed with H2S saturated water behind it into the water column.

How does sufficient SO4 get into the deep bed quickly enough to build up the H2S levels faster than H2S can diffuse out? Honestly, I have not idea. Perhaps the saturation levels are not very high. Perhaps SO4 travels faster than H2S through water. It is a difficult question I really hope somebody else addresses before I do some research and reinterpret it into my brand of pseudoscientific BS!

What do we do about this H2S? I would have said just to be sure about your sand being compaction resistant and planting lots of rooted plants. Due to the interesting feedback from folks with mixed substrate layers and substrates like clay with very fine grains, it seems that part of the answer is to have a substrate bed which is proportionally shallow or deep to the grain of the substrate(s), with fine gravel being VERY DEEP (larger gravel would be impractically deep) and clay or soil being shallow. I hypothesize that because of the geometrically slower rate of diffusion as grain size and thus the interstices of the substrate become smaller, capacity of the substrate bed may diminish unless other factors keep the interstitial size proportionally much larger than grain size i.e. unless something keeps it fluffy, the substrate bed's capacity shrinks as its grain size shrinks. This is just an educated guess. I think soil keeps its porosity high despite the small size of its grains. Interstices are spaces in between things, a good word to know. Interstitial is anything of the nature of interstices. Porosity is an effect of the quantity and size of interstices.

OK, I'm too sick to play the windbag anymore. It's just that dissolved gasses and diffusion are so strangely fascinating to me and so important to the aquarium in general and the functioning of the freshwater DSB in particular.

g'night!:dance2:

 

[DeeDeeK]

Oh, I think I must have misstated myself about CO2 and airstones/bubblers. The effects of a stream of bubbles rising to the surface are to a) bring water from the bottom to the surface of the tank, where it can absorb O2 (water equilibrates its O2 level with the atmosphere rapidly) and b) agitates the water at the surface which actually drives off CO2, up to the point where the water's CO2 content is balanced with the CO2 content of the atmosphere. Water for some reason does not exchange CO2 with the air nearly as readily as it does O2.

Here is a link, maybe a little hard to comprehend but it tells the tale of agitation and CO2.

Oops! forgot to include this: http://www.hallman.org/plant/booth2.html

Here is a brief video of a filter with its inlet near the bottom of the tank and its outlet positioned so it disrupts the surface with water from below without agitating it - this ensures more than adequate oxygenation in the great majority of aquarium setups/stocking levels while not blowing off all the CO2.

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And though it may be a bit cumbersome reading, I suggest this link: http://en.wikipedia.org/wiki/Partial_pressure as a good bit of information about gases dissolved and not, in equilibrium, etc. I'm trying to find the information about the rate of exchange of oxygen between water and air - which is rapid due to the high partial pressure of oxygen which pushes O2 into the H2O- and the exchange of CO2 between water and air - which is much slower due to its low partial pressureunless accelerated by agitation. All this despite the fact that CO2 is much more soluble than O2 in water (by 24x) and diffuses faster through it.

The whole agitation thing is about two factors at work, as I understand it. One is surface tension disruption - surface tension in water is from the fact that water molecules latch onto one another and let go rapidly, all the time, with what is known as a hydrogen bond, making water very resistant to being a gas despite its low molecular weight (were it not for their hydrogen bonding, water would be a gas until very low temperatures). Well, in most of the water, the molecules can grab onto one another in three dimensions, up-down, side-to-side, and back-and-forth. At the surface, they only have 2.5 dimensions: -down, side-to-side, and back-and-forth. No up is available in the up-down dimension so the molecules end up latching together more frequently and more at a time in the side-to-side and back-and-forth and -down dimensions, which causes there to be a much more tightly knit couple of layers of molecules, in tension. The second is molecular movement; shaking up the water molecules as agitation or heat do causes hydrogen bonds to break more frequently and lowers the capacity of the water to hold gases in solution as well as allowing the water itself to more readily escape as a gas. So warmer water holds less of any given gas and so does agitated water.

This is purely my layperson's interpretation of science literature I read so long ago I cannot remember where to find it in order to double check or cite it, so forgive me if I am scrambling some of this. Thermodynamics and chemistry are not my strong suits.

Back to surface tension, molecules, agitation, water, and gases: SO, when gas molecules which can form h-bonds with H2O (like CO2) approach the layer of surface tension (with its densely knit water molecules), they are confronted by a barrier which they are sucked into but cannot pass through to the atmosphere very quickly relative to the rest of the water though they can move from the air into the water very readily. Agitating that barrier disrupts the hydrogen bonds of the water molecules in the surface tension enough to let bigger molecules through more quickly as well as brings a supply of water not yet depleted of said gas molecules to the surface to give them up. In other words, shaking up the water lets the CO2 out faster.

But what of O2? Ah! The O2 molecule does not bond with H2O that it slips right through the molecular blockade of the surface tension. Heating water will cause it to release its oxygen more readily because the H2O molecules don't hold on to each other as tightly and knock around with greater and greater speed 'til they're bouncing the dissolved gas molecules right out of solution, but agitating it will not break enough hydrogen bonds quickly enough to send the H2Os careening fast enough to knock molecules out of solution unless you were to agitate it extremely quickly, knocking the molecules around so rapidly it would be indistinguishable from heat. Actually, it would be heat.

So, since CO2 is so soluble, you can dissolve far more CO2 than its equilibrium concentration with atmospheric CO2 and it will stay in solution for longer than, say O2, because it latches onto H2O molecules. Open a bottle of carbonated water very slowly and only a little CO2 comes out of solution and forms bubbles. There're scads more CO2 in solution than the partial pressure of atmospheric CO2 will hold back. Only its solubility in H2O keeps in from erupting. Agitate the water and the CO2 is dislodged from its hand-holding with H2O and emerges as gas rapidly. Same deal as in a fish tank.

Since O2 is so relatively insoluble, not depending on chemically interacting with H2O to stay in solution, it will tend towards equilibrium with the partial pressure of O2 in the air, agitation or no. Thus as water is depleted of O2 and brought into contact with air, equilibrium will be rapidly restored. The high partial pressure of O2 in the air causes this to happen quickly despite the low solubility of O2 in H2O. Bring water from the bottom to the top where it can displace the water within the surface tension layer (which is at equilibrium with the atmosphere) and it becomes oxygenated as quickly as any bubbler can oxygenate it.

I can't believe I just burped all that information up! I bet 80% of it is correct at least!

Honestly, I share all this because I hate airstones and air pumps ever so much... Tacky and loud, I say.

I set up a 5 gallon (thought it was 7 for a while) tank and took the internal filter from the 9 gallon, and reinstalled the 9 gallon's 170 gph overhead filter which I had to downgrade by putting a perforated piece of plastic in between the powerhead and its outlet. But this caused the water to squirt and splash, agitating it. I didn't worry about it but in the last month I've noticed more and more my eichhornia diversifolia has gotten skinnier and skinnier stems and leaves, my milfoil has been weakening or not growing at all depending on species, and some plants just plain quit growing and then started losing leaves. I couldn't figure out what I was doing differently!

Well, I finally narrowed it down to the overhead filter. So, I moved the perforated plastic from being between the powerhead and its outlet to being between the powerhead and its inlet so the water reaching the outlet would be under low pressure and not squirt and splash. Then I packed filter floss and foam through the overhead filter, which had been a wet/dry setup so water would flow evenly without splashing to the filter outlet (different from the powerhead outlet, which is inside the overhead compartment) and I filled the tank with water right up to and over the filter outlet so there's only a mild turbulence at the surface.

The filter is the only variable I can figure out to have changed and the plants weakened, so now it's been changed again and I'm betting the plants will strengthen.

Righty-oh! Time to go. Enough said!

oh, I'm feeling a lot better, if my volume of writing didn't tell y'all that already.

 

[Anoxia]

That was a very thorough explanation, I will definitely refer to it every time I have questions about dissolved gasses. Now my problem makes even less sense, though. You recommended that I should turn my canister filter's spraybar upwards, so the surface got a little agitated, which I did, and it's probably helping, but it still isn't enough to allow me to go very long without bubbles. I read that hypoxia can also be caused by eutrophication, meaning too much nutrients in the water I think, so that's why I had blamed it on the decaying organics. Now that I think about it, though, if my water was very eutrophic, I would have lots of algae, when in fact I have very little. I think my tank is basically the Walstad type, so maybe I should just buy her book, and see if she addresses this.

Switching topics, I stuck the roots of a Pothos plant in my tank just for fun (I have an interest in aquaponics), and it started growing these massive leaves! Look at the diference in size between two leaves right next to each other on the same vine. You can see the roots hanging in the aquarium below.

"

 

[DeeDeeK]

That was a very thorough explanation, I will definitely refer to it every time I have questions about dissolved gasses. Now my problem makes even less sense, though. You recommended that I should turn my canister filter's spraybar upwards, so the surface got a little agitated, which I did, and it's probably helping, but it still isn't enough to allow me to go very long without bubbles.
Possibly, the problem is still excess CO2. If the spray bar isn't agitating the surface sufficiently, it will not drive off much CO2 though the turnover of the surface water will make for good oxygenation - I'd be surprised if there were sufficient oxidative processes occurring in your tank to use up the O2 faster than it can be replenished. I'm not saying it can't happen but I am saying it's unlikely. Eutrophic water generally doesn't have good turnover of the surface water. In many human-created ponds in Florida, a big fountain is installed to blast CO2 out and turn over the water to bring O2 in because otherwise they become warm, stagnant, and eutrophic - O2 deficient, CO2 excessive, and very fertile.

I believe the spray bar is sending sufficient water up to the surface to absorb O2 but not agitating the water enough to release CO2 into the air. The bubbler causes sufficient agitation to drive off CO2. If you can place your spray bar above the water so it's output splashes into the tank, it will drive off the CO2. Alternately, the is insufficient O2 and the volume of water that needs to turn over at the surface to absorb enough O2 to replenish the tank is more than your spraybar can deliver. A rising column of bubbles draws water up with it to the surface, where it will absorb more O2 than it does from the bubbles (bubbles don't have lots of surface area) or so I have read but haven't researched. If that's the case, you can find out by increasing surface turnover without inducing agitation - i.e. get rid of bubbler and use another filter or powerhead to send more lower water to the surface without agitating it. If that fixes the gasping fish problem, the problem was O2, which you'll know because the CO2 is not being driven off so it's still the same concentration as it was prior to the bubblers and powerheads/filters. If the fish are still gasping, the issue is CO2, which you'll know because so much water will be turning over and getting oxygenated.

Sheesh, I wish I could be more succinct!






I read that hypoxia can also be caused by eutrophication, meaning too much nutrients in the water I think, so that's why I had blamed it on the decaying organics. Now that I think about it, though, if my water was very eutrophic, I would have lots of algae, when in fact I have very little. I think my tank is basically the Walstad type, so maybe I should just buy her book, and see if she addresses this.
YES! YES! Buy Walstad's book!


Switching topics, I stuck the roots of a Pothos plant in my tank just for fun (I have an interest in aquaponics), and it started growing these massive leaves! Look at the diference in size between two leaves right next to each other on the same vine. You can see the roots hanging in the aquarium below.

"

Your water is nutritious! Walstad says roots can take up CO2 - maybe that's a factor in the Pothos' growth. Also, terrestrial plants tend to prefer nitrates, which your water ought to have. Oh, and if you dose fertilizers...well, duh. Oh, and the dissolved organic compounds your aquarium water doubtlessly abounds in can chelate iron, manganese, and other metal/mineral nutrients and keep them available to plants - I learned this from the Walstad book. I wouldn't want to drink from that tank! Or any tank! Too bad whenever I siphon them, I get a mouthful!

It would be great if you had an O2 and a CO2 testing kit! I want them for myself, to be able to settle questions of oxygenation/CO2 saturation clearly.

 

[Anoxia]

Hey, I just realized something, looking at this picture of the top of my tank... do you think the glass lid is causing the oxygen shortage? It has open spaces in both the rear corners for the filter intake and outlet tubes, but maybe that's not enough.

I'm scared to take it off though, because I had a rainbowfish jump out last night. I turned off the light in the room, and heard a thumping noise, so I turned the light back on, and my poor fish was behind the tank in a cardboard box full of aquarium odds and ends. Good thing he didn't land on the carpet, or I wouldn't have heard anything. I think he got scared of the sudden darkness, and just happened to jump where there's a space in the lid.

I've heard splashing before when I turned the light off, but this is the first time one of them made it all the way out. I'm not really sure how keep my flying fish contained, while letting more air reach the surface of the water. My sister suggested a mesh lid, but it seems like that would rust. Ideas?