I run two Aquaclear 70 HOB filters (w/AC50 impellers, set to low flow) on my 60g. Way back when, one was filled completely with a mixture of Seachem Matrix and DeNitrate while the other was just mechanical media. These days, both are totally filled with stock sponge and bio-sponge material. In spite of the marketing to convince us we need expensive bio-media materials, I feel sponge material is the best material for both mechanical as well as biological filtration. In a sense, my filters are HOB sponge filters!
Having 'said' the above, many hobbyists add additional filters to their tanks with the thinking that "there's no such thing as too much filtration." I feel that this is a MYTH. Good filtration is about how well we filter water, NOT how much water we push through filters. If we filtered every drop, REALLY WELL, say 2x/hour, you'd have crystal clear water. There is also something to be said about biological filtration as it relates to one or more filters. BB populations are relative to the available food and O2. So regardless of filter capacity, the BB population is indirectly controlled by the amount of ammonia in the system. Ammonia levels will be relative to the stock load and feeding and will be even less in the planted tank. Besides, in the established tank there is a LOT of BB in the substrate and on decor.
So you could add another filter of a similar size OR upgrade to a larger one.
Note: For HOB's don't invest in a cartridge filter. Fluval C4, Aquaclear, and Seachem's fairly new Tidal ALL allow you to customize the media as desired.
