In the past I've used nothing but the Hydro-Sponge II's and have always considered them extremely effective, but a massive eyesore at the same time. I also have floating plants that tend to collect around the lift tube outlet and block surface movement from the far sides of my tanks... Anyways...

I just received a (4) pack of the dual sponge filters off ebay for a 5 gallon tank I'm setting up in my office. (I ordered 4 because they cost only a fraction more than a single filter). To see it in action I put one in my 5 gallon bedside tank that also has a Hydro II. I was extremely impressed by how the 90 degree elbow at the top creates far more water flow than the Hydro II's I've been accustomed to. I began to think about swapping all 11 of my tanks at that point... . Currently I run 2 Hydros in opposite diagonal corners of my tanks in an attempt to have massive filter capacity and theoretically, flow throughout the tank... However, like I said, the straight up and down lift tube has it's weak points. I'd consider elbows, but that would be even more of an eyesore... I also love the fact that the dual sponge filters don't need a flat area to sit. I aquascape my tanks and have had to work around this requirement...

Anyways, Currently I'm running the new filter in addition to the old one so I don't completely remove the bacteria colony. My question is, how long should I keep the old filter in the tank? Can I just pull the old one out when it's been a few weeks or so? or should I ring it out in the water? cut it up and perhaps shove like half of it in a hidden spot for an additional period of time? I also figure on the tanks with two of the Hydros (8.5-11.4 gallon tanks), I can replace one with a dual and eventually replace the other with a dual once it's been a few weeks or so...?

My tanks contain nothing but shrimp for the most part... I'd just prefer not to have any fatal mini cycles while swapping to the dual sponges. Any advice would be appreciated...