Instagram hashtag help

Hi guys I have been using the IG hashtag strategy of 8-10 large nices (up to 1M), 8-10 medium nices (up to max 500k), and 8-10 small (less than 100k) with limited success, and now my engagement is dropping. I have also been changing most hashtags (although keeping brand specific ones so IG does not think it is a spam account. Would you please advice as to how you guys use hashtags?