Well, some news. We decided to trust the room safe. We have been here 5 days. We did money inventory tonight from the safe as it seemed unreasonably thinner. We are missing $900 from the safe. We had asked for no maid service until today, the people next to us say they have seem maids at our room numerous times, but they really didn't pay much attention. At any rate, someone has access to the master key and has been slowly tapping out cash. The reason we know is because my spouse keeps a daily ledger of our cash expenditures every day on every item, no matter how small.
We just found out tonight, have messaged the hotel manager, and will talk to her in the morning. Trouble is with no proof of who took it the cash is just gone. We would ask to be refunded the rest of our stay and relocate, but literally everything is booked.
So..beware. The room safes are not safe at the Posada Arco Iris! This lesson is on me.