I have been working hard to create a zoo in my sisters Minecraft realm and built a large aquarium for dolphins 30 block diameter circle ten blocks deep with coral, sea weed, and sea grass. I used the seaweed to make sure the entire aquarium pool was source blocked water and had the glass come up three blocks over the water line but left the top open air. I get the dolphins into the aquarium and every time the swim around all over the place but never surface never jump for air so after a few minutes they suffocate. Nothing's blocking them there's lots of open water and they never seem to get stuck they just stop trying to surface and die. I've tried coral and no coral, deeper water and shallower, higher and lower walls but every time I witness within ten minutes they just so trying to surface and die.