If I'm lookin' at this correctly there may be one problem...
. Is the Eheim intended as the return pump? I considered this years ago myself and was informed the canister will yield poor results as there is no gravity feed to the inlet of the canister. That gravity feed "boosts" the output, that was the theory. This may be wrong but something worth considering...
I agree with going parralel. U-tubes are a pain and unreliable. Take it from me, NEVER do the "temporary thing"...
