Thinking of adding a 2nd filter to our 20 gallon tank before we add any more fish. I have been using aqadvisor.com to help with figuring out what my tank can hold and such and it is recommending more filtration before adding any more fish. We currently have a marineland penguin 150. I was thinking of adding an additional penguin 100 which would for sure cover what I need but is there something else I should think hard about going for? Or staying away from? I was wanting to to go the 2 filter route since my tank is cycled and I don't want to lose what is on the bio wheel in my current filter.