The Emerald Crab is a superb algae eater, and probably one of the very best at cleaning eating Bubble Algae. It is very useful in keeping reef aquariums clean. Large specimens can be harmful to small fish and invertebrates although this is less likely if there is sufficient algae for the crab to eat. Maintaining proper Ca, Alk, & Mg levels is important for growth of their shells.
Don't forget about your water parameters when combating algae blooms. Water chemistry is every bit as important as a good clean-up crew.
It is important that proper calcium (420-440 ppm), alkalinity (8-9.5 dkh - run it 7-8 if you are carbon dosing) , and magnesium levels (1260-1350 ppm) are maintained. Raising magnesium levels gradually up to 1400-1600 ppm can help to combat algae outbreaks, just keep CA and Alk in line as you raise the Mg. Nitrates should be below 10 ppm and phosphates should be below .10 ppm. We recommend doing a water change when Nitrate levels rise to 10 ppm. It is important to replace your phosphate media when phosphates rise to .10 ppm. Media Reactors make the most efficient use of your phosphate media by fluidizing it.
Vivid Aquariums uses and recommends dosing pumps to automate the dosing of additives and keep your levels more constant. A dosing pump can alleviate the chore of manually dosing your aquarium with Ca, Alk, & Mg 2,3, or 4 times per week and will benefit your aquarium by keeping your levels constant through frequent small additions of Ca, Alk, & Mg. Our tanks all progressed when we switched from 3 manual dosings per week to 70 automatic dosings per week and we got a lot more work done.
If no algae is present in the aquarium you may supplement the Emerald Crab's diet with live macro algae, dried seaweed (nori), or mysis shrimp.