I live in Santa Cruz. Nearby is the UC's Long Marine Lab, I was thinking about contacting them to see if they could provide me with filtered sea water, or at least point me towards someone that could. I don't have an RO unit, but here's what I'm thinking:
Currently I have 2 freshwater tanks setup adjacent to each other (a 100g and a 40g), sharing a filtration system, inhabited by two turtles. The turtles are going to move into a stock tank (like a big plastic tub), to free up the glass tanks for a ceph. The octo is going to live in the 100g, and I'm going to treat the 40g as an emergency reservoir, so that if I need to do a water change I'll be able to do a 40% easily. I was also going to pick up a 30g trash can or similar and use that as well. Am I being silly? Is it better to just go for the RO/DI unit?