Can I add a pair of yellow watchman gobies?
Yes, they change sex. They may or may not pair up, just like people sometimes it clicks and sometimes it doesn't. Starting with two small ones is the safest bet. Even if they are paired, the will not spend all their time together.
The watchmen will generally pick a spot and stay there, while the diamond will move throughout the tank. The diamond will likely learn to avoid their area.
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