Hello all... was wondering if you could help. Was here asking questions over a year ago and everyone was so helpful and patient!

I've got a small, six-gallon tank with six copper rasboras. We've had them for just over a year now. Yesterday (or possibly late the day before) I noticed that one of them has been hiding behind the filter and acting very frightened. He (she? I have no idea) comes out once in a while, but is always timid now. I should say, these guys have always been a little flighty... they don't like you to watch when they eat, they don't like the light turning on or off, I think they actually recognize us outside the tank and scatter when anyone but me approaches the tank (temperamental or what). This is very strange, though. This guy who's hiding seems slimmer to me, too, but I'm not sure if that's because I'm looking for something to be wrong. I'm not sure if he's eating or not because I have to stand so far back for them to actually approach the food that I loose track of him when he comes out. He'll swim around if I put my hand behind the tank where he is, but he goes right back when I leave. I tried turning the filter off for about 20 minutes to see if he'd come out, but it didn't seem to make a difference. I've used my test kit and all levels [pH, GH, KH, Nitrite (0) and Ammonia (0)] are exactly the same as they've been for the past year. I create lots of hiding places with their driftwood, plants and rocks, but they rarely use them and prefer to hide behind the filter tube when scared.

The only recent change has been their food. All our pets get stockings at Christmas and the fishies got new food, too. Previously I was giving them plain old stuff (TetraMin Tropical Crisps) and occasionally brine shrimp flakes (Nutrafin Max Plus, flakes plus bits of freeze dried brine shrimp). The new food is Nutrafin Max, small Tropical Fish Micro Granules. I thought I'd try these as I was having to crumble up the crisps so small for them to eat, tiny little guys they are. I thought the food should be transitioned gradually like with any other animal, so I gave them bits of both over the last two weeks until they were up to 100 per cent new food. This is the only thing I can think of that would correspond with the behaviour change in this one. But why didn't it affect everyone if this is the cause? Perhaps this one little guy just doesn't like the new food and hasn't eaten in a few days? I just don't know enough about fish to hypothesize. I tried feeding the old food today, but I don't think he ate any.

Any insights? I don't want to lose the poor guy.

P.S. If anyone remembers me from back then, we've been having a great time with the little aquarium setup. They sit by my desk now as our daughter's initial enthusiasm has waned. She's three, so I expected to be their primary caretaker. They're remarkably tough little creatures. We've had two instances where they've jumped the tank (that hole has been plugged now) and I've been able to scoop them up and throw them back in. Within a few minutes, they were good and I couldn't tell the jumper from the rest. Unfortunately we lost what had been number seven while we were away in September as the gal doing our chores didn't notice one had jumped until it was too late. :( The six that are left don't swim together really anymore, but otherwise seem alright. I hesitate to add a new one in the other's place as the tank really is quite small already and I'm told six is still at minimum for these fish.