Given the poster's question, the advice would be to do many water changes, frequently, like every other day if the top soil was place in there recently.
If the top soil is 3-8 week or more old, then you can relax.
Sediment vs water column:
Plants can do both, I know of no plant that cannot take nutrients from the water column.
A few cannot take nutrients from the sediment and they lack roots.
However, adding nutrients to both locations, especially when you want to address wimpy plants that die easily for most folks, is the wiser approach.
This way you get more out of both locations.
So add ferts to the water column and the sediment.
As far as pantanal, R macrandra etc, these have long been grown just fine in plain sand and good water column nutrients, folks have more trouble with CO2, not nutrients than anything(95% maybe more of the issues stem from poor use of CO2/too much light).
Nutrients are easy, add ferts consistently
(this is the harder part for folks especially when they have poor CO2 and high light) to both locations over a wide range, as long as they are consistent
, and add a nutrient rich sediment.
This gives you the best chance of success and the bases are covered.
Do not fall for that "do not dose the water column" advice.
You do not gain anything in doing so and only force slower growth(which is not what you want in the first, the plants are doing poorly if you are asking and one of the ironic claims) and more limitation, as well as more draw and less life out of the sediment.
I am always scratching my head when folks ask what is limiting in their tanks and they suggest not adding ferts
If you want less growth, use less light.
You might not need to add ferts in your tank with lower light and good CO2, however, other folks might have more light and less CO2 and that, not the nutrients, is much more likely the issue.
This is going to be more true with wimpy plants.
Also, there's little consistency in the type of soil: % organic matter, N and P, clay content, which as anyone could guess, would influence growth.
This does not matter if it's soil, loam, ADA aqua soil etc or any macro rich sediment. So it's wise to have a back up, the water column.
This way you can rule out nutrients, cover all the bases and hedge the bets you are providing adequate nutrients everywhere.
From there, you can focus on CO2 and finally light to modulate rates of growth.