Crawdads will eat anything and believe me, they have better eye site than you expect. I had one that would grab and chase a pencil around the tank. Not much smell there. The one I had loved to eat nightcrawlers and cooked popcorn shrimp as well as spinach, shrimp pellets, leaf lettuce, algae, plants and anything else including trying to eat the tubing for his bubble wand as well as the bubble wand. I have also fished for them and they will grab a spinner as fast as they will grab a piece of fish.
As for the F8, I have a friend that has one in a 10 gallon and has for 2 years. I guess the tank is brackish, he adds the normal amount of salt, 1 tablespoon for every 5 gallons. He also feed it crawdads so chances are a blue wouldn't stand a chance unless it had a lot of places to hide.
