Well I bought it for my sucker to occupy since he was running out of room with the floor of 75 gallon being heavily planted. Unfortunately my good intentions killed it.
It is a 20 gallon long. I want to use it as a hospital tank in case one of them gets sick. How do I keep it running and a bio filter sustained? Should I have it inhabited by something and then move them to the main tank in the event I have to put a sick fish in there and medicate?
I personally would resist the temptation, in my time of grief & guilt, to christen the new 20L as "Sucker Memorial Fish Hospital," but would instead set it up for routine ongoing operations as "Water Park #2 for Some Smaller Fish I Really Like."
My recommendation is influenced by the following thoughts (YMMV):
* how regularly do you expect to HAVE sick fish ?
* how often to sick fish actually get better, sufficiently so that one is willing to return them to live with the "regular population?" (My track record not good; if salt dosing doesn't do magic, I go quickly into damage control mode. I understand Other People may have acquired better fish medic skills. Or at least the pleasant illusion that they have fish medic skills.)
* keeping a bio-filter sustained for a
possible sudden fish load is a nuisance. Counting on the fact that it's "fully charged" to step up is another element of risk to an already shaky patient, or group of patients.
* there's a significant chance that any medications or cures you try will kill or compromise the bio-filter too.
* for an emergency yet totally flexible fish hospital, use a bucket or a cooler, with an air line, and just do 50% water changes daily. Or if the fish isn't too big, an Utz pretzel jar.
So ... turning to the happier side of this experience .... what kinda fish are you thinking of putting in that new 20L? Of course, to MAXIMIZE the fun, it is also
NECESSARY for you go at least 180 miles, and meet some other NANFAns, to get these fish. Hey, Spring is almost here!
HTH - d.d.