Your water temp seems pretty standard issue as most cichlid keepers(barring discus) have their temps between 78-82 degrees. The water changes are key, as you mentioned but I don't think a lone fish will emit hormones that will be detrimental to its own growth. Good luck raising your dovii...a beast in the making for sure. "Power Feeding" will only shorten the life of your prized dovii...it is not necessary to feed as much as you are regardless of the quality of food that is being given.