I have a 65 gallon tank that I have had up for about 3 to 4 weeks.. I didnt know that you werent supposed to put a bunch of fish in it at first and I baught 12 and they slowly have died off until I have 8 left. I found out that I had an ammonia problem and have been doing a partial water change every other day and it seems to be getting better but my female guppies are turning almost black from tail to their mid section.... they are all pregnant is it normal for them to be turning black....