Hi
That is one of the most complex questions of a planted tank. lol Everything works but has limitations. In my last setup i used 4 inches of top soil with an inch of small gravel. Got fantastic growth fron rooted plants in particular but after 8 months shows signs of slowing down.
IMO probably one of the best is straight flourite, sold as a substrate. Expensive but is very good all around.
As you can imagine top soil is good but difficult to settle. Not sure it's worth all the effort long term but does provide fantastic growth. This is a 150 gallon with an automatic water change system which is why I tried it . A small tank would be too difficult. You could try that as a layer but be ready for cloudy water.
Peat works also but tends to turn the water amber,Not harmful . If you use peat be sure and boil it first much easier to work with. Don't try it with top soil as you will have nothing left lol.
I've tried every combination possible over the years and find that 2 years is the most you can expect no matter what you use.
You can find much discussion of this subject on the KRIB ,waterpplants site . gary

Florite is most likely the best there is as Gary said. I don't put any soil or peat in my tanks anymore because it really doesn't help. Well at least not long term. The one thing I have found that has impact is the size. Even inert gravel makes a good substrate after it has "matured" from fish poop and the like. Good size is 2-4mm, like Profile and Forite. I have a 55G with 100% Profile, the only problem I have with it is weight. It is very light and doesn't anchor new plants or cuttings well. Profile and Florite have allot or iron and other nutrients in them so you don't have to supplement for root feeders as you would with inert gravel. Here is a link to the chemical breakdown of some substrates. My suggestion is mix some darker inert or even Florite gravel with the Profile, if anything for looks and weight. Other then that 100% -50% Profile with 50% antthing else is good. Soil just drains and clouds the tank when doing maintainence.

Here is a link that might be useful: Substrates for the planted Aquarium

Now, I don't understand why some links are allowed and others aren't!! Everytime that I've tried to post a link to the detailed information about my Palludarium contruction and the specifics of the substrate(the most important factor!), I'm refused and if I even mention it, it,s harshly deleted! I've been a member for several years, lurked using a family members membership before that and the info on "My Page" is open and detailed. I'm not selling, buying or even trading anything and am confused as to when GW became so nasty about this! Even the letter that I got back from them, in response to one that I sent, was rather cold!! They won't even allow me to send a private email if I try to include a link! If you're interested, send me a email and I'll send the direct link to The Orchid Source. It's the only place that I ended up detailing exactly what I had done! I had originally wrote the details for my native fish group! Thanks!! Scott

You could always put the web address in the text portion and people can copy and paste it to the address.

Ok, thanks for the input. I have a 20 gallon tank, so some of the indepth stuff will be more difficult. (Im going with a 120+ when I buy a house, so this is practice!) I think I will use about 1/2 profile, 1/4 florite and 1/4 small cover gravel for looks. See what that does. After reading in other places I should keep the sand out. Even though I realy like the looks of it, Im shure my plants and plants that I have died, will grow well with out it.

Thanks.

I have put the web address in the text portion and my individual post has been removed from the discussion every time! I wrote a letter to iVillage and asked why my post were being treated like this and was told that links to other sites were NOT ALLOWED! I thought that checking it out there would be better for them here, as well. I wouldn't be using a big chunk of their storage space with large photos and info. If you're still interested, go to the above mentioned site and pull open Orchid Soup, then scroll down to 'Palludarium/Vivarium answers!'. It was done in response to quite a few requests for details on why my plants were healthy(Both the aquatic and the terestrial plants.)Scott

After I had already posted, I did more than just skim your letter! I would encourage you to go ahead and use the sand!! I've also read many posts on many websites critical of the use of sand. I realize that everyones conditions, etc, are different but, personally I think that they're wrong. I have never had any of the issues with using sand that I've read. The sand does need to be on the deep side and the bigger the system, the better. If you look at my photos and explaination, you'll see that all of my water is pushed to one side. I have a hidden particulate filtration (refugarium) area. This is just an area screened off using my old under gravel filter plates across a back corner. The sand is swept clean by the current and I never vaccum it. Many of the negatives that I've read about have never occured. My system has been up and running for a few years now. I added a completly active/living system with plants and the fish went in next! Bam! No waiting, no anything! I've had fish since the early eighties and tried everything and it doesn't get much better at this point! I have at least half a ton of black gravel that I bought over the years. It's being stored along with my wet/dry filters that I used for my Africans and all of my other huge power filters. I'm very, very happy with the performance of this one! Scott

Thanks Scott for trying with the link. Heres what Im going to attempt. Ill do 1/2 of the tank of the above 1/2 1/4 1/4 mixture and the other half Ill lay sand over top. Ill try for the edge of an eco look.

If I do find that one side grows better than the other Ill post back. Thanks every one for the help.

O.K. I'll try to post some photos in the gallery section! I hate to do so because I have to reduce them to a ridiculesly small size considering the amount of adverts that you have to put up with! Really, if you will go a have a look at the other photos and read the explaination, you'll have a better idea of what I did!!