[WallaceGrover]

Can someone explain to me how gravel, which I would think has much larger particle sizes than sand, is anaerobic while sand is aerobic?

 

[JasonG75]

Because air can get in and around gravel whereas with sand air can not penetrate it.

 

[plantbrain]

Neither case is anaerobic.............

If you put 12" deep of sand or gravel, different grain sizing in a plain tank with water, wait 5 weeks, they will have the same O2 level on the bottom of the tank.

In a planted tank:

What determines O2/redox is the % organic matter and the loading of this matter into the sediment and the flux of O2 from the particle size, plant roots which actively add O2, "burping up" of CO2 from the sediment every so often etc.

So you can have highly anaerobic conditions with gravel.........and aerobic conditions with plain sand..........

 

[WallaceGrover]

Hmmm, I was reading Walstad and she said gravel is deadly to the planted tank because food rots in the gravel anaerobically...

 

[plantbrain]

Hmmm, I was reading Walstad and she said gravel is deadly to the planted tank because food rots in the gravel anaerobically...

Needs more than gravel alone to cause ANYTHING...........I can grow plants fine in plain sand, we all can..........or gravel. Gravel would have less anaerobic conditions than sand, there's less to block flow between the lower layers.
Old fish Food = plant food.

 

[DarkCobra]

Hmmm, I was reading Walstad and she said gravel is deadly to the planted tank because food rots in the gravel anaerobically...

She also says:

"In my experience, tanks with pure gravel substrates are hopeless for growing aquarium plants. Then, because the plants don't grow well, the gravel needs to be vacuumed and algae becomes a problem."

Of course, if you add the correct fertilizers to the water rather than the substrate, many plants grow very well. And they develop good enough root systems that the gravel can go months or even years without vacuuming. Plenty of tanks out there to prove it, including some of mine.

Much of what she says is only applicable to her own style. If you're not adding fertilizers to the water, as in a Walsted-style tank; then yes, I would agree that gravel is hopeless.

Seems a lot of people don't understand that though, and incorrectly try to generalize her advice to other tank styles; resulting in a lot of confusion and misinformation.

 

[Ziggy]

+1 to that. This is an insanely complex hobby with infinite permutations, and even attempts to duplicate setups is like chasing the wind sometimes.

I once had a 10Gal with plain department store (coated) gravel, no ferts of any kind and in that setup it fluked out that a twisted Val I shoved in there not only grew but propagated like crazy.

I will say though that while sand "scares" me in terms of its potential for anaerobic bacteria development, its double edged: just as its more difficult for O2 to get down into it, so to is it more difficult for waste to do so. The finer the substrate the more the waste sits on the surface. After I switched from course substrates (like reg Fluorite) to a very very fine gavel (though not quite sand) I was shocked at how little waste I would pick up during water changes (even digging down deep with the siphon tube). I think my affection for corys is a factor: with a fine substrate waste tends to sit on the surface and their constant rummaging stirs up most of it into the current which eventually takes it to the filter.

 

[zdnet]

Hmmm, I was reading Walstad and she said gravel is deadly to the planted tank because food rots in the gravel anaerobically...

She was referring to gravels larger than a certain size, NOT all gravels. From "Ecology of the Planted Aquarium":

"The gravel used to cover the soil should be fairly small (2-4 mm). . . . Stones or pebble-sized gravel should never be used. Not only is the larger gravel inhospitable for plant roots, it can endanger the fish. (Uneaten fishfood trapped between the pebbles can rot anaerobically and pollute the entire tank, possibly killing the fish.)"

 

[plantbrain]

Some tank scapes it would not matter though.

But in general, this is correct.

 

[zdnet]

Some tank scapes it would not matter though.

But in general, this is correct.

One of the very important aspects in Diana's book is the explanation accompanying its recommendations. Together those explanations help people to think through a situation. People are no longer restricted to paint-by-number. Because of the explanations, people can apply what they've learned to a wide variety of situations.