Small Blue Starfish

Hello

I have countless hundreds of these small blue starfish in my tank:

http://www.garf.org/STAR/starfish.html

Ive tried tweezering them off every week but they still just keep
multiplying. Ive read that harlequin shrimp eat starfish and thus ive come to
the conclusion that i need one. Has anyone else got a shrimp or these
starfish?

Am i supposed to buy the shrimps in pairs?

Also i will need a supply of starfish to feed them after they (hopefully) eat
all the small blue ones. What do you suggest?

Thanks

Warren

PS ive got a Scarlet Hawkfish in the tank and wonder in it will pose a threat
to the harlequins