Plenty of pre mixed saltwater.. and a vat or tank big enough to hold your whole system. So not only your 150 and 265, but another shallow wide at least 250 gallons for the swap.
I changed out a 280 to a 500 2+ years ago. And forgot about extra holding water. You will not only need the difference but an extra amount to hold the livestock while your refilling.
Time, it will take 2-3 time more than you think. Once you pull the plug, you can't stop till your finished. If this is your first attempt at changing tanks. It's not like setting up a new system. You can't do a little work here and there. You will need everything for the change. Nothing like finding out at 1:30 in the morning your one fitting short. Or some new equipment doesn't fit right, short pipe, wrong pipe etc.. You must plan every little detail.
My change over took 3-days and about 60+ hours
Also 5-6 buddies help alot..
Good Luck