here are the answeres to your ?s
1. any amount, preferably an amount that your fish can eat before they go bad.
2. if you get them frozen get a cup of water from your tank and let them thaw then drop them in the tank for the fish, a fishes stomach is the size of its eye. for example i have a couple of dalmation mollies and i give them 2 or 3 each.
3. i would get frozen because if you keep them in the freezer they stay good for a good period of time and when placed in the water the current from your filter causes them to move making them apear alive and tasty to the fish
4. yes they could very possibly sink under the sand so it is important not to overfeed ( back to ? 2 )
good luck, my fish love them and im sure yours will too.
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