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Re: Dark Substrate



Some idle thoughts on the subject...

There are dark substrates that are OK, but be a bit cautious in this 
area. I tried some beautiful black sand that glittered. It was growing 
big tomato plants at the gravel-supply yard when I bought it.

Unfortunately, it was probably copper slag and ended up apparently 
killing some rare pupfish when I didn't do quite enough water changes. I 
tested it on other fish, first, but it apparently was only slightly 
toxic (zero reading on a Dupla copper test at all times). The brackish 
water may have been a factor, too, IDK. [They were a very difficult 
species, so I'm not even positive the substrate caused their death.]

Dark colors in minerals often comes from metal oxides. Iron forms red, 
brown and black oxides. Some copper ore is a beautiful dark brown, 
almost black. Other is turquoise blue or bright green. Well-oxidized 
iron is fairly benign, biologically, but copper salts may not be. Other 
heavier metals, like lead, are a real problem and are found in beautiful 
rocks. The heavy metals may be pretty fully oxidized and hence fairly 
harmless. [That was what I thought about the copper slag, though.]

I don't think the "acid test" (soaking in Muriatic acid) does much good 
with such materials, so try to be sure you know what you are using.

One thought I had for a "cheap" substrate was to just use filter carbon. 
It is available for bulk industrial use pretty inexpensively. It might 
need to be boiled to drive off air (so it will all sink) and to rough 
purify it for the tank. You could not treat it as casually as normal 
gravel, for it will tend to soak up any toxins, medications, etc., and 
slowly release them back into the tank. It is probably worse than peat 
in that regard.

What would be really nice would be if someone would bring in volcanic 
beach sand, that had soaked in ocean water for many years and been 
ground to rounded shapes by the waves. Black lava (basalt) is, I think, 
mostly inert aluminum/magnesium silicates/oxides with iron oxide as most 
of the pigment. It would be great for substrate material.

Anyone living up North of here near the Columbia plateau may know of 
black river sand deposits that would be even better than beach sand 
(fresh-water soak being even more solvent than salt water).

It could make for good trading material for NWK!

Wright


-- 
Wright Huntley -- 209 521-0557 -- 731 Loletta Ave, Modesto CA 95351

"The right of self-government does not comprehend the government of others."
                                 -- Thos. Jefferson --

That's what Independence Day is all about, isn't it? <www.self-gov.org>


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