Welcome to the wonderful world of float flying nervegrater
The object concerning center of gravity when converting to floats is to maintain the exact same center of gravity after the floats are installed as it was when flying on wheels. And as noted by Jim B. above most installations after floats are installed require some weight added forward to return to that same CG when on wheels.
Now a key point in this situation is do not add the weight to the airplane in the nose. Instead add the weight to the bows of one or both floats. Its easy to just drill or cut out a little chamber for shot to adjust the CG and simply add a monocoat or tape patch over the hole. This is the one time I say it is preferable to add weight ballast rather than moving stuff around inside the airplane because now if you have done it as above it will not be necessary to rebalance the airplane every time you change between floats and wheels. Cheers.
John