I always admire that one in your signature. How long has it been up? Do you have a filter in it if so (i think i saw one) what type? How often do you perform water changes? Sorry about all the question i am genuinely interested not just trying to get info out of you to tell you that you are doing something wrong. I was thinking about getting a similar setup...actually the exact same tank.
Jayderana
I have had my tank since beginning of April its called a penpal, they come in various sizes i think this is the biggest size. Yes it does have a filter its a Fluval One Plus and i do almost a 50% change once a week with a vaccum.
Jams. alaskan
My danios seem to be very happy, I wouldn't provide them a home any smaller though, my LFS had a setup similar to this but with additional 2 goldfish, I FEEL that its toooo much.
My filter has a very strong current and my guys love to skim it at the top right hand side where its at its strongest, its like they are having a race...lol, or when i come into the kitchen they all crowd around there waiting for me to feed them, they are so funny. When the evening draws near they quieten down and like to surf the gentle current towards the back next to plant on the right hand side, its like they go into some sort of "trance" and just stay still in one place and gently surf its interesting to watch.... there are many places to hide and settle at the bottom like under the filter or towards the back left or middle, or round the rock on the right and well they love to play chase especially the "tail nipping game", there is plenty of room to scoot around (seriously) they are very fast active and humurous to watch.