You've answered your own question....

Fluorite....I have a 250L tank with a thick substrate (100% fluorite) and
havn't looked back. I will never use anything else. Except perhaps Onyx
(which is the same but black). Personally I would not bother layering the
substrate. The fish will disturb it anyway and the fine sand will sink
through the gaps in the fluorite and gravel and make their way to the bottom
of the tank (well in theory they will).

The only other solution would be to partition the base of the tank and have
areas where ther fluorite will be concentrated (these being the places you
put the plants that need it the most).

Personally I would go for 100% fluorite.

"Laulose" wrote in message
om...
I am starting a new tank, and I need some help with selecting my
substrate.

I have decided (based on past experience) that I need some sort of
iron supplement in my tank, so I chose to do a partial substrate with
Fluorite. In addition, I would like to use some white sand and pool
gravel. I am hoping to get away with just one bag of Fluorite. (20
lbs.) I will layer the bottom approximately 3" with my substrate,
with no undergravel filter, heater, etc...

I will be building a high rock shelf in the entire background, and my
plants will be all grasses. (with the possible exception of something
that attaches to the rock shelf)

My lighting is 110 watts, I have pressurized CO2, no fish for now, and
it's a 45 gallon tank. (I have no water parameters right now, as it's
not set up, but excepting the iron deficiency, my water has
historically been well within all acceptable limits)

Thanks alot!