The raw Shrimp will decay and be a continuous source of ammonia for the bacteria that you need to grow in your tank before you add fish. You should research fish tank cycling before you get going. If I was better at the stuff, I'd be able to give you a link to it, but I suck at tech. Lol. So, google tank cycling and read up on the nitrogen cycle. No more than 2 clowns in the tank or they'll Fight. Most tang need a bigger tank than you have to be happy. There are some bristletooth tangs that would be ok In a 70g tank though, so research those. Best thing you can do is do a lot of research on the fish you're interested in. Go to liveaquaria.com and look up fish, that site tells you their temperament, size tank they need and there's also a compatibility chart on there. Lots of reading involved.