I set up my tank just over a week ago. Is a 30-40% water change every other day enough on a 6 1/2 gallon tank? It's filtered and has an air stone. My 2 guys are showing a little stress and it's worrying me.
So, they are in a divided 6 gallon? Is it truly cycled, or are you doing a fish in cycle at the moment? You aren't changing out your filter media, are you? (that kills the cycle since the bacteria live in the filter media). If it's divided, they've got about 3 gallons each. I'd be upping your water changes to 50% a week at the very least.
I have no idea what amquel is. I'm guessing it's some sort of bottled or powdered bacteria that supposedly helps cycles... Personally, I think it's not going to do much, but if it's meant for cycles, I don't see why you couldn't dose the tank.
Amquel Plus removes ammonia, nitrites and nitrates from tap water. I'm not a cycling expert but you do need nitrites and nitrates as part of establishing the cycle I think. The end result should be zero though. More of a cycling specialist can probably tell you more.