stock tank sump

i dont have a pic of mine but i run the 70g stock tank for my 120. i dont have any baffles in mine and have no bubble issues. definately want to replace the stock bulkhead. as far as an ATO i just made a holder that hangs over the lip of the tank that has my float switch, that switch runs the aqualifter which pulls water from my 5g storage tank through another container with Kalk and then into my stock tank. I didn't have the RO feed directly to my stock tank. (although i did for a bit cause i had a leak in my kalk container and i over filled the sump and lost 95% of my coral) my return pump is just sitting in the bottom of the tank. I use an external recirculating skimmer as well. i also have cheato in my sump as well although its not in the best way possible as it dont "roll" like its suppose to i guess.

 

I use a 100 gallon stock tank as a sump as well. Like snowman82 said change the bulkhead. I made a holder for a filter sock holder out of pvc fence post and used silicone to attach it so i can hang it in the sump. You can find these fence post at menards in the garden section outside. the one i used is abought 2 inch thick and 4 or five inches wide. I was told silicone wont adhere to a stock tank but it did for me. Just make sure you use aquarium safe silicone
I use a external pump that sucks water out of the bulkhead. I also have a screen over the intake so i dont suck anything large into the pump. You should'nt need any baffles. I don't have any problems with micro bubbles. Just make sure when you plumb it use true union ball valves and plent of unions so you can easily work on things if you need to take anything apart.
As far as the auto top off i use a dual float swith from autotopoff.com. I just hang it on another holder i made out of the fence post. I just run a water line from my ro into my sump. I use 2 solenoids to stop water flow. I have 2 just to  act as a back up in case one fails, you can get these from autotopoff.com as well. I've been told this is a bad idea running it from my ro but it hasn't caused me any problems.