My ballasts stink! Need a lighting solution!

I think iv'e read something like that too, however, the first post says that the bulbs are 15" 18 watts than in either way, the ballasts are over specked so I would expect it to work. somethings not right.
 
My 18 watt bulbs are about 8-9"... Do you think I should purchase 24 watt bulbs and see if the ballast will work correctly that way???
 
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