sump design?

The restaurant tank I take care of is driving me nuts.  I try to battle one thing and another problem shows its ugly side.  One problem is that the sump that was made for the tank is too small.  Im conjuring up a thought of making use of a couple of 55gal drums I have around.  I have at least two.  One currently holds top off water and the other is empty.  I would fabricate one into a sump and use the other for water top off and changes.  This would increase water volume a little bit and maybee even give me more room in the closet space I have to work in.  Any thoughts on this.  I have also thought of using a large  stock tank but I think it will be too big for the space I have to work with. 
Josh

 

Evaporation is not the issue. Im just considering the use to get more water volume and make use of what little space I have. Im fighting hair algae at the moment. Ive added GFO and Carbon and they have worked a little. Im thinking now that my problem is with sludge build up in the low flow corners of the tank.
Josh