As a rule of thumb, Aqua Ring is a no-no. In the turn you took to activate Aqua Ring, you could have gotten off a Recover (which is a must for Milotic). It nullifies the Burn damage if you turn it into a double wall with Marvel Scale, but leaves you exposed after a good pounding. If you're that intent on getting a 1/12 regen from Aqua Ring each turn, have Vaporeon Baton Pass one over to you, along with an Acid Armor or two and, if you're in need of health, Wish.
By the way, Vappy is pretty awesome for supporting Milotic late game, when you've taken out nasty Electric sweepers like Electvire. Against special attacking grasses, Vaporeon can take a hit and, giving its high special attack, probably do a fair deal of damage with ice beam.
Edit: whoops, misread that.
Milotic needs a second attack move to deal with grasses and vicious dragons like Garchomp and Salamence.