I guess it would depend what your fish stock load is going to be. If your going to be running a skimmer as well? On the Rena link I gave above it gives you the product info. It says "recommended for an aquarium up to 175 Gallons". So I would say one should be fine for your 135gal.
Yeah I love the Rena. I got mine used from someone who posted on the buy and sell forum. People sell them & the Fluval when they decide to drill there tanks. I was lucky & got the Rena for $80. But I tell yeah, well worth every penny if I had to buy a new one.
