Well.... some have said the zinc in the galvanized layer leaches into the water and harms fish, but others dispute this. I think Id be inclined to put in a liner unless the tank was old and the galvanized layer and/or manufacturing oils was worn off. Is it possible to have it in the garden amongst the plants so you can view the fish from above and the plantings would conceal filter &plumbing pipes. You could have the water returning to the tank via an old spigot or pump spout

Thank you so much for your input. I might put the tank in and let it cycle, then test water. I'm in no real rush as my husband that area tied up with his deck project. I'll try to post picture of his work. It's going to be a great addition to our home!

Goldfish are pretty resilient. They are offended by lead - it will kill them, but they can tolerate small amounts of copper (which kill koi). If you use any metals with them, do it sparingly, but do not include any lead plant wraps (as used to band together underwater oxygenating plants. Galvanized may be ok. I suggest you put in a couple of test feeder goldfish and wait to see if they are ok (anywhere between an hour and a week- for leaching purposes as noted by kashka above), or if they start swimming strangely. If they're not perfectly happy, your problem with the metal tank will only get worst unless you paint it with EPDM paint or line it. Also, if you return water to your tank via a tap of some kind, the same metal warning applies. Make sure too, that you don't have asphalt shingle run-off from your roof going into the tank. That's a whole other problem. I love my 1/2 barrel water gardens with goldfish and mini waterlilies in them. Good luck!