First, try adding a one way air valve to each of the tubes on your system. They come with the petco pumps. Otherwise, they are about $2 at an aquarium store.
Second, make sure your tube is submerged under as much water as possible. If it is curling back up on itself and is therefore only a few inches below the waterline, attach something rigid to it.
If that isn’t the whole problem, try this. Take the whole Airlift tube system out of your bottle. Detatch the needleside portion of the air tubing from the little one-way valves. Blow through those air tubes to clear all the water out. Maybe leave it out to dry and if you see any waterdrops in the line. You want to try to dry out the air tubing part of it and have air pumping through it before you stick it back in the pre-filled bottom water bottle.
Here’s the logic. Water is going to want to get in to the air tubing through the needle. If it does, that water is a lot of extra “weight” that the pump has to counteract to get it’s air out of the tube before it even makes it to the needle. So dry that tubing out and then only reinsert those “guts” after you have hooked it up to the pump and the pump is on. This way it is always blowing air out so water can’t get back in.