Hello, I'm new to the forum and am looking for some advice. I live in Maine on a lake and have a permanent dock that I've been deicing for 6 years. I have a Vivosun 102W 1750 GPH commercial air pump. Until this year I used the manifold (10 connections) that came with the pump. While it worked OK all of the connections are barbed and tended to vibrate off resulting in me going into the lake to fix it. I've built a new manifold and am not getting air flow to all the stone diffusers (9) that I was with the old manifold. Below are some details. Any advice is greatly appreciated.

1) Vivosum 102W 1750GPH commercial air pump
2) 9 - 8"x1.52 cylinder stone diffusers.
3) The manifold is built using 1/8" brass fitting and 1/4" Sharkbite connectors for the 1/4OD tubing. The manifold has 5 connections left and right of center where it connects to the pump. Each connection does have a shut off valve.
4) The pump is in a custom box under the crib that the dock is built on.
5) The longest run from pump to diffuser is 16' and the shortest is 3'.
6) The water depth varies but during winter month is 1 - 2' closest to shore and 4-5' furthest from shore.

I am getting good flow through one diffuser, the one connected to the last position (I'll call it 5 Left for discussion purposes) on the manifold on the left side which is the 2nd closest diffuser to the pump. I am getting minimal air flow from position 4 Left but not enough to keep ice out and no flow for the other 7 diffusers. I wasn't having this problem with the "barbed aquarium diffuser". Apologies for the long post but thought details would help.