I have just set up a bio orb 30 litre tank I left it for a week to allow the water to settle then introduced 4 guppys 2 male and 2 female all of the fish died within 24 hours the only thing I noticed that was odd was that they swam around as if they were drunk !! can anyone advise me of the cause of this might be. I have tested the water and it appears to be fine,