Running a tank with no fish & a filter gives you an uncycled tank. Put anything but some hardy livebearers or danios in there & you will probably have problems.
I keep extra filters running on most all of my tanks, and have an extra 28, 20, & a couple of 10's empty, along with spare heaters. I could set one of these up in 20 minuites.
I also keep a 10 with chlorinated water,an airstone, & a heater at the same temp as the rest of my tanks. If anything needs immediate attention, or I get a phone call at work from a family member, a squirt of dechlor & toss in the fish.
Tolak