Iron plays a similar role in low-tech societies as co2 does in high-tech ones.

[myric]

I'm not trying to burst anyone's bubble here, but let's get real - adding extra iron only boosts plant coloration if your tank was lacking it in the first place. It's not a magic solution that replaces CO2 or anything. If you're seeing pale leaves, that's usually a sign of iron deficiency, so upping the iron levels will obviously improve coloration.