In case you want to keep him, here’s what I found he would eat:
Ulva Lettuce
Some varieties of Red Gracilaria.

I order mine from http://live-plants.com and keep it in a small 10 gallon alge tank, adding some for the sea hare as needed. I’ve kept mine for 6 months in a solana nano.

Ill try and be brief in answer to your questions.

1. nope the sea hare doesnt need to be submerged – quite often mine has its head out the water.

2. Purchased food – hmm – nope ive never seen it eat anything – even un eaten fish flake food that is on the sand…
so sorry it would only do the algae.

Would just mention that you need to be aware the shrimps will pick on the sea hare – and can depending on how often happens drive the sea hare to climb out of the tank – or die if they really pick at it.

but to temper that statement they are hardy creatures so mostly will just hide and the 2 cleaners shrimp i had get bored easily and it just hides its head until they leave it alone…

but then it did climb out of the tank once – and thanfully its thought better of that since then …

firstly, i understand the need for aclimating but i’m also dubious about adding lfs water into my tank. do you need to keep the seahare submerged and lastly would you be able to keep us updated on its survivably on purchased food?