I used sand from the landscape place, cleaned it really well and it was not very cloudy at all. If you clean well, and it takes AGES, you shouldn't have very cloudy water at all. Fish won't mind anyway.
I did this when I changed my 4ft cichlid tank from shingle to sand. They were quite happy in there for a few hours. I had the heater running in there as well.
I have a large rubbish bin and lid (kept only for fish) for these sorts of things, I catch all fish and put them and plants and filter in there, do the tank put the water, plants filter and fish back in and all done!
I don't think a silver shark is a good idea. They grow fast and big. One of mine has grown to about 7inches in 10 months. They grow to around 12inches. I have mine in a 600litre tank.