Help with closed loop ...

I attempted to build a closed loop system based on Marc's directions
(http://www.sparklingfloorservice.com...losedloop.html).

The deviations I took are as follows:

- Using a Eheim 1250 pump instead of a Mag 5

- return from pump to SCWD is flexible hose (not PVC). This was due to the
return hole that was available in my tank cover ...

- my SCWD is lying on flat, not vertical like Marc's.

I used PVC cement where I could, and took effort to make everything
air-tight. However, no matter what I do, after some time I get micro-bubbles
.... whenever this happens, I can see the air bubble through the flexible
pipe so I think it has to do with the pump sucking water from the tank.

Is the Eheim 1250 not a good substitute for the Mag? Is it because I'm
trying to suck the water out, but the run is too long? I have similar
dimensions from the intake tube to the pump ...

Or, is it because the SCWD is on it's side? I read the instructions and I
thought it didn't matter ... however, not sure if I'm imagining this but I
think I hear the SCWD's internal gears and am afraid I'm putting too much
strain.

The other thing I was thinking was that my seals are really not tight, and I
should re-do the whole contraption ...

Any help would be appreciated.