On Tue, 16 Dec 2003 04:40:24 UTC, Ben wrote:

Hey all,

Was wondering something the other day. Now I know that to keep
plants happy in a tank you want to keep trace amounts of iron in the
tank. Now here is the thing, the house I live in was built in 1923 and
has old iron pipes. Now is there going to be enough trace iron in the
water or am I going to have to add it. just wondering

Very unlikely that the iron pipes will do you any good whatever. You'd
think, when all you need is a tenth of a part per million, it would be
easy to get that much iron; it can't be THAT insoluble! Well, it is.
Iron in the ferric form (Fe+++) can't dissolve in fishtank water, or
drinking water, even in parts per Billion. Ferrous (Fe++) can, but it
oxidizes quickly (if there's enough oxygen that the fish don't suffocate)
and drops immediately out of solution.

Rusty pipes will put rust particles in the water, but not iron in
solution. Rust in the substrate might be useful to plants, but adding
laterite is probably better.

So how do you get iron in water?

1. Iron in the ferrous (Fe++) oxidation state can dissolve, but it
disappears quickly; I've tested and measured this. It probably would
stay in solution if you kept oxygen out of the water. Joke.

2. The ferric state (Fe+++) dissolves just fine in water that's far too
acid for fish to survive even briefly. Ferric chloride, FeCl3, is soluble
-- but if you neutralize it to pH 7 (or 5) the iron drops out.

3. Chelating (key-lating) agents like EDTA and HEDTA grab the ferric ion
and keep it away from the nasty little OH- ions that would make it
precipitate; and plants can still extract the iron and use it. Sorry
about iron and ion; I didn't invent the language.

--
Dan Drake, a freak who compounds his own chelated trace elements

http://www.dandrake.com