plant tank filters

i am going to be constructing a Wet/Dry filter for my 90 gallon 
community tank and was wondering if this is the best choice for the 
plants and the fish?  i was thinking of using 5 to 9 gallons of bio 
balls, is this enough, what are some good brands?  

also has anyone that has ever built their own wet/dry had any 
problems with the water from the siphon emptying too quickly and 
overflowing the sump tank, or the pump running too fast and then 
ending up running dry?  any suggestions about other potential 
problems would also be great.

        rlknight at rex_smumn.edu