Freshwater Deep Sand Bed (DSB)

[Anoxia]

As the organic detritus sinks into the DSB and is eaten by bacteria, oxygen is consumed. The more detritus, the more O2.

That's what I thought was causing my fish to gasp, till you told me about CO2 excess. I was glad to hear that, because low oxygen would have been an ironic problem for a girl whose forum name means, "no oxygen", LOL.

I found a link to the "anoxic filtration" method gaining popularity in koi keeping, it uses clay, but it is in baked form (kitty litter) so you don't get the turbidity problem that regular clay can cause.

http://www.essexsection.co.uk/html/anoxic_filtration_system.html

 

[Anoxia]

I found a pair of two-part scientific articles written by a man named Robert Toonen, Ph.D. that discuss particle size in depth. Here's the first, I know the primary topic is plenums, and it is mainly saltwater, but we have no choice but to look to saltwater if we want to learn this stuff, because that's where all the knowledge on this subject has been up to now. Part 1 and part 2 are equally good, do yourself a favor and read them both: http://www.seabay.org/art_plenums_part1.htm

The second two-part link I wanted to share, is an experiment that Dr. Toonen did on different depths, and particle sizes of marine sand beds. Suprisingly, the results indicated, "it doesn't appear to matter a whole heck of a lot"! Enjoy: http://www.advancedaquarist.com/2005/6/aafeature

 

[DeeDeeK]

always, if I contradict anything you know to be true, DeeDeeK, (or anybody else) please correct me!

The same, I'm sure! Or perhaps I should say "Ditto!"

I've thought a lot about using bisqueware, or rather bisqued (low low fired clay that's basically sintered together, not fused as in higher temperature firings) either crushed to a small grain size as a substrate, or simply to make decor which would also serve as biofiltration once colonized by those good bugs we all love so much.

Perhaps the clay body could be mixed with short polyester fibers as is done in some sculpture and fancy-pants pottery throwing. The fibers would burn out and leave voids, upping porosity.

 

[Anoxia]

Have you looked into expanded clay products, like the kind used in hydroponics? I think they are made by a company called Hydroton (or Hydroballs, I can't remember). My LFS uses something similar to it their planted tanks, but theirs is smaller and finer, like "Grape Nuts" cereal size. I should see if they sell it, I bet they do, and I bet it's pricey.

Laterite is baked clay, too, much like kitty litter, but I think it has different minerals because it's red, probably lots more iron. I just used plain old red art clay in my aquarium, because as a sculptor, I have a lot of it already on hand. As long as you have sand on top of the clay layer, it cuts way down on turbidity. The only time I get fog is when I uproot plants.

I could see using sand as a bottom layer, with the expanded or baked clay product as your top layer, or else you could mix a baked clay, or expanded clay product with fine sand (like Reptisand) to fill the huge interstices. I wish I would have thought of that recently when I redid my pico. Dumb move to go through all that trouble of planting my pico right before my Walstad book arrives. I'm sure I will want to start over once I read about all the things I've done wrong, LOL.

 

[DeeDeeK]

OH! I was actually thinking of red art clay because I wondered if the iron in it couldn't slowly leach out were the clay bisqued. You know, zeolite isn't exactly a clay but it's very close to clays and feldspars chemically. I've thought about a zeolite substrate, which would chemically adsorb ammonia, nitrates, nitrites, minerals, all kinds of good stuff which then would be available for bacteria and plant roots to access.

Anyhow, I've thought about buying grog from the ceramic supply place near me - cheap and meshed for size, rough texture so therefore greater surface area - though not porous. I think it would work great though maybe be too sharp for cories and loaches.

As I understand it, artificial aquatic soils like ADA brand stuff or "Flourite" and a few others are baked, sintered together like bisqueware and/or have fritted nutrients (minerals fused together into a glass, only very slightly soluble in water). Aqua-Soil brand aquatic soil, however, is based on a water absorbent polymer. I'm not really into any of them because a DSB will grow very fertile on its own without special substrate so why spend the money?

Kitty litter is just baked clay? I never knew. I guess the cheap, unscented, otherwise untreated stuff is what you'd want. Cheaper than grog I dare say.