Burp the canister.
When you think the canister if full of water, take a flashlight and look for the waterline on the canister. If you can see a waterline that means there’s air in it. To get the air out, unplug the canister, and then release one of the clamps holding the top on. Let a little bit of water spray out through seems, then close tightly. Now plug it back in and let it run for about a minute. You might have to do this 3 or 4 times if there is air in the hoses. The quicker you can unplug the canister then release the clamp, the better.