Pump Causing Microbubbles

I'm going crazy! I just set up my new tank, 36gal bow with 10gal sump/fuge, using an Eheim 1260 return pump. I have discharge side of the pump valved halfway with about 4' of head. I have the overflow line (drilled tank) go into a 200 micron bag in skimmer section. I am not running skimmer. I have over/under baffles before return section of sump. I am getting tons of microbubbles returning to tank! Would the pump be too large for the tank, even valved halfway, and contributing to the microbubbles?

 

There are several ways to eliminate micro-bubbles in your sump, You need to determine where they are coming from. The most common sources are from 3 main culprits:
1. Protein skimmer (which you dont have running)
2. Low water level or splashing over baffles
3. Exceptionally high turnover of the sump

If it's low water or poor sump design, then you need to take corrective action in that way. If your return pump is overpowering the size of your sump and turning it over too quickly, then you just gotta throttle back if safe to do so for your pump, and if not replace the pump all together. From what I see it may be a little too big.