My top 3 choices for Aqua Patch:
Lapras-GX
Lapras offers a lot of card draw on it's own, so being able to consistently Aqua Patch is a realistic option.
This helps the deck recover from Grunts and Hammers, as they usually run a rather low Energy count (approx. 10 Water energy, and you need 3 to attack).
This also synergizes well with Manaphy, as you can retreat to either Patch on energy, or reset your Blizzard Burn.
M-Gyarados
Mega Gyarados scales based off of the energy attached to him, and discards from your deck while he attacks; I feel the synergy here is obvious.
Wishwashi-GX
Kyogre accelerates an absurd amount of energy from your hand, and Gyarados can accelerate it from your discard...
but you still need a place to put it!
Along with it's massive HP stat, Wishiwashi gives you a different attacking option for your deck, preventing you from being walled by things like
Giratina,
Regice, and
Glaceon.
It's GX attack also OHKOs a lot of other Pokemon, while setting up your Gyarados/Kyogre!
With Manaphy in play as well, it's nearly risk free, as you can retreat after.
Keep in mind that we may be losing Float Stone next rotation, and Field Blower was recently printed on top of that... so Manaphy may prove to be a rather invaluable card~
Nice to see another Primal Kyogre player but what will you be swapping out for it? Currently running 3 max elixir and 1 mega turbo. Either way, there are so many options in the upcoming set to make Primal Kyogre more fun to play with!
I don't think you need the Max Elixirs or Turbo, as Kyogre's main strength is accelerating from the hand!
Try using Professor's Letter, and Aqua Patch (in this case) is almost strictly better than Mega Turbo.