My first and biggest mistake, so far, in my sort time working with aquariums, was trying to change my gravel substrate to flourite without removing the fish. I took out the plants and put them in a bucket, lowered the water level, scooped out the old gravel and started to dump in the flourite. I didn't rinse or wash the flourite first and the dust immediately turned the water into a dark brown cloud - I couldn't see a thing. I had no idea how long this clould would take to settle and couldn't finish my work in the tank, because I couldn't see the fish (or anything else).
I panicked and began to net the fish and toss them into another tank, without any preparations or time to acclimate them to the new tank. I lost a few fish that day, although not as many as I thought I would.
Anyway, unable to give you the proper advice on how to do this transfer, I can tell you how NOT to do it.

I panicked and began to net the fish and toss them into another tank, without any preparations or time to acclimate them to the new tank. I lost a few fish that day, although not as many as I thought I would.
Anyway, unable to give you the proper advice on how to do this transfer, I can tell you how NOT to do it.