Haddonis are somewhat dangerous to other fish, especially if they are clumsy swimmers or disoriented.
If you keep your polymnus on their own or with fish that know how to navigate anemones (Banggais for example), I would not hesitate to add one.
But haddonis don't mix well with bottom dwellers like gobies, jawfish or dartfish to name just a few.
BTW, how big are your polymnus?
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