Good job reading up, that's definetly the way to go!
The Richard Ross book is virtually identical to the aqualog book so if you've got one you're pretty set. I wouldn't put the rays in that small a tank especially when you have bigger tanks available. You will only need to move them quite quickly. They will last a good while in your 180g or even one of the 120g's. Do you mind if I ask where you are getting these rays from?
I would highly recommend not buying a ray smaller than 5"disk as a first ray. The added expense of buying a slightly larger ray greatly increases the chances of the ray surviving. Very small rays are extremely delicate and despite your fishkeeping experience there is a strong chance of you losing one (or both) at that size.
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