Mythrax in my Reef

[ZBT3091]

About 6 months ago i bought 6 mythrax crabs for my reef. After i got a sand sifting cucumber and saw a mythrax pinching it and removed 5 of them and put them in my sump and 24 gal. Right now I have one mythrax I can easily get in my sump, the other two have been living in a jungle which is my 24 that is algae central. I saw one of them yesterday and it is a gorilla its at least 4 inches across! Im thinking that if I add the other 3 mythraxs they can really do some damage on cleaning hair algae that I have in my 75. I have since gotten rid of the sand sifting cucumber who seemed to be fine, and got a huge tiger tail that is weaved in and out of the rocks and rarely ever comes out. The one mythax that I couldn't get out from the original 6 that i got stays in one crevice in a piece of rock and never comes out even at night he stays within an inch of the hole. Im thinking I should add the 3 to fight the hair algae. Is there usually a big risk with mythraxs and cucumbers?