Aquaforest oceanguard display tank water level problems

[johnmac28]

I am ready to pull my hair out. I got a new oceanguard 275 about 7 months ago. I have never been able to keep water level correct. No matter what, I get it stable, then within a day or 5 at best, ato goes off too much and display is too high and of course salinity has dropped. I have read everything I can find (no air bubbles affecting tunze 3155 sensor, I change socks every 2-3 days, etc). Return pump is a red dragon.
is this happening to any other Oceanguard owners?
What am I missing?
maybe gate valve problem?
Attaching pic of sump setup.

 

[blaxsun]

Where is your ATO and where is the water being added?

 

[johnmac28]

ato container is integrated with sump on right side. Ato level and return are in return section. I have supply line from ato above supply to avoid siphon. Pump setting on tunze is dialed down to nano setting.
anything sound off there?
Thanks for your reply.