definitialy get a test kit. 3'x1'x1' is pretty big for that small of an aro if your quarantining it. i have my baby aro in a 10 gal (18"x12"x12") only filled half way. when i did have it filled all the way he was so confused and couldnt catch a guppy, but now that its lowered he is happy and is working on his aim (still not a good shot, but getting better). i also had a Bio Wheel 200 on the 10, bad idea. so when water level was lowered, i put in a sponge filter and its been smooth sailing since. just make sure that you do a water change every day like it is your life that depends on it.
im also a fan of Melafix, it hits so much junk its awesome. you might try that if your aro still isnt doing good...just as a preventative measure.