I changed it about four days ago, on Tuesday. I use Aqua Plus tap water conditioner. I have PRIME too, but I use that for my 88 gal.
Sometimes he's active and then he just hangs out in the little rock formation or behind plants.
I just got a little filter from Doctor's Foster & Smith website, and it's an amazing little filter. It doesn't make a current and it was really cheep and very very quiet. His next water change is next Tuesday. I read that you should change it once a week if it's filtered (since it's a small tank)
This is the filter I bought:
AZOO Pam filter It's amazing. I actually got up last night to make sure it was still working it's so quiet XD