Mercs are typically quite recluse but will learn a regular feeding time. A trick for a merc house (and it has worked for at least one other dwarf/small octo) is to find a cluster of giant purple barnacles (no varnish!). Set the cluster so that an octo sized opening is about 1/3 of the way up the tank (I have both embedded small clusters and used larger ones that meet this height suggestion). Females seem to gravitate to them within 24 hours and stay denned. Males will move about but still use one or more much of the time.