tests are looking good. and get that refractometer, it's always good to know where you are at.
As far as emerald crabs, i dont have one, but i want to get one down the road one day. I hear mixed reactions all the time about them. Love em or hate them. I cant give you my honest opinion since i dont have one but you can always get one and try it out, if it doesnt work out for you, go trade him back in. I guess they will attack your other critters if not well fed. Here's a small description I found off of ***********.
The Emerald Mithrax Crab is well respected for its scavenging ability. It will enthusiastically feed on uneaten meaty foods and many types of nuisance algae. Unlike many other animals, Mithrax sculptus will eat bubble algae and helps clean your aquarium of these algae. Its distinct, flat shiny green body and hairy legs easily identify the Emerald Mithrax Crab.
Native to the reefs of the Caribbean, the Emerald Mithrax Crab is nocturnal and hides in caves and amongst rubble during the day. In the home aquarium, this member of the Majidae family requires a well-established aquarium with plenty of rockwork and hiding places. Once familiar with its surroundings, the Emerald Mithrax Crab will venture out of hiding during the day to forage on algae.
Care needs to be taken to ensure an ample supply of food is available for the Emerald Mithrax Crab. Many aquarists supplement the Emerald Mithrax Crab's diet with dried seaweed and chopped meaty foods, such as shrimp, as well as a quality pellet fish food.
Otherwise, this opportunistic feeder may turn to corals, invertebrates, or small fish for a food source. However, when well fed, most Emerald Mithrax Crabs are very tolerant of their tankmates and highly compatible in reef environments.