I recently bought 7 white Mountain minnows, 5 zebra danios and 2 plattys. I have a 125l tank and just started this hobby. My minnows don't really swim around and come home yesterday found 1 dead and today I found another 1 dead. My danios and plattys are swimming around actively and look healthy it's just my minnows that just floating. Anyone know why this is

Hi

As this is a new tank, did you do a full fishless cycle with ammonia before adding fish? If not, then you are cycling fish in and the minnows most likely died of ammonia poisoning. The rest of the fish will be at risk until the cycle is established so you should follow the advice on this link: https://www.fishkeeping.co.uk/articles ... ammonia-nitrite-spike.htm

I have done a test and the ammonia nitrogen is okay

The aquarium shop said the hardness of the water is genuinely hard down here so that's normal too