test for ammonia that will tell you right away whats going on .I always keep a bottle of ammonia lock just in case , you can dump some in and not have to panic about doing a water change right that second.

If it was a large turbo the shell should be seen somewhere and if there is nothing left then no worries, if it's dead in the shell then remove it fast as that can mess your tank up royally.

Also if you're thinking of upgrading do a 75g which is the same length as a 55 but abit wider and taller. For a mid size tank a 75g is the best all round size, 90g is abit tall and unless you like getting wet to the armpits the 75 is a winner for mid size.

Damn turbo
 

I found him in the fuge in the middle of the chaeto.. Put him back in the tank.