More Info please:

Did you yank them out of the water or did they come out on their own?
Did they crash as soon as you we're airborn?
Did you fly for a bit and then crash when landing?

Trying to diagnose this off of your letter, is tough.

Do you have any Pics of your plane float set-up?

Basically flying off floats is LITTLE different than wheels, EXCEPT!

The Plane is now heavier, bulkier, and a lot more weight is below the wings. So Minimise your Acrobatics until your used to the new handling.

Also make sure it doesn't try to lift off the water too soon! (too much AOA) and (heavier remember). So with out sufficient air speed you will tip stall and or wallow around in the air like a sick duck.

Use Full up elevator to get it on step when you 1st crack the throttle, about a second or 2. then relax the elevator until it has
sufficient speed. (You have to steer with the rudder here).

IF your set-up is right? it should "lift itself" off the water, or if power is low then you may have to give it a little up elevator. Be sure to be ready to relax this as soon as it breaks free of the water or it will climb too quick, and may stall. and a stall at 2- 5 feet up is not good. it would probably either drop straight down, or tipstall, roll over and drop in wingtip 1st. either one is bad.

Hope this helps. It is all I can give with receiving more details.
Smoky.