i wish i had a reference handy for this but I'm quite certain I read a conversation or letter from Srila Prabhupada where he said that the harmonium should not be used during Arati. Rather the devotees should stand up and chant accompanied by kartals and mrdanga.ekendra:
As far as standing up or sitting down, dancing with mrdanga and cartal is best, and Prabhupada mentioned this in the letter.
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