[Betta132]

I may be getting a fairly large order from Liveaquaria, tetra-sized fish. I need to QT them, of course, so I need to cycle a QT for that.
My 65g is running two 55-rated HOB filters, both with two cartriges each. How many cartriges would it be safe to move? The tank contains mostly small tetra-ish fish, about 30 total, though there's a nice big female checkerboard chiclid in there. The tank is lightly planted with a big handful of dry oak leaves all over the bottom, and there's a bunch of spindly branches all in there.
My other option, I suppose, would be to use that store-bought bacteria stuff.

 

[garfieldnfish]

You can move 2 cartridges without problems. I have changed out that many for new ones plenty of times. If you are worried about a sudden drop in good bacteria just feed a little lighter for a few days. But bacteria are not just in the filter cartridges but all over every surface of your tank and in the substrate. It won't take them long to recolonize the new cartridges.

 

[Betta132]

Okay, good. There's that problem solved!