live sand

Before i say anything else, this isn't a bristleworm or anything i've EVER seen before. It's a decently large centipede looking creature that I kind of think is an isopod of sorts? It moves very strange, almost like a shrimp swimming, and didn't appear to be hostile but was apparently hungry...

i would like to set up a native northeast saltwater tank.. I'd like small local fish as well as crabs and sand and mud....... I'm in info collection mode... I'd like a 75-90 gallon tank..... I'm looking into required filtration..... I'm worried about flooding my basement, so what type of filter...

Hi all. I just got my first tank set up yesterday. However, after doing more reading today, I may have made an error. I added the live sand to the tank, then added my tap water, and then added the salt concentrate, and mixed it all in the aquarium. Did I accidentally kill the live sand? No fish...