[IUnknown]

IMO, its more than just the bacteria, although thats a big part of it. I don't know how much of a problem it is with eco, but with onyx, you have to get through silicates causing brown algae for about a month. Your plants will also take about a month to reestablish enough of a root system to air-ate the gravel to move the nutrients from the water column into the substrate. Floating plants can help while the tank stabilizes. My most recent journal,
http://aquascapingjournals.com/journals/18_gallon_onyx.htm
been about a month and the brown algae is no longer a problem, still dealing with some hair algae on the glass.

 

[IUnknown]

Dennis,
Another thing, you might want to consider using flourite, depending on how high light the tank is. Over 4wpg and dosing iron in the water column doesn't help as much, and you need to have more in the substrate. I am using onyx sand and will switch back to flourite because of this.
Flourite™
Iron 18500 mg/kg
Onyx Sand™
Iron 2846 mg/kg
Eco-Complete
Iron 41,600 mg/L *I don't know how kg and Liters relate so this number doesn't help much.
If you look at this website,
http://home.infinet.net/teban/jamie.htm
it has Eco Complete at
Iron 4,170 mg/kg
but flourite is a little off, so I don't know how accurate the numbers are at this website.