I had several floating plants weighted down in the sand and they did extremly well. but about a month later, the plants all rotted and died. they all did it at the same time too. now i have gravel. what went wrong?
What's your lighting? Is it in the 10 gallon? The light that comes with a typical 10 gallon hood is just enough for low-light plants and not much else.
I would of thought most floating plants require to float as they get a lot more co2 from the air and light as they're nearer the lamp. The dangling roots act like mini-bio filters as they consume nutrients like nitrate and phosphate. They should grow more vigouroulsy floating and can also provide shelter to some fish.
I have a floating plant, riccia, that is kept as a ground cover. This plant needs a lot of light, especially when attached underwater, so that may have been your problem. I have some in my 10 gallon with 65 watts of light! It does great with high light and CO2, but I doubt it would do well without both.