I would wait for the air to completely bleed. It is not possible to tell from this picture whether you are using a 90 degree elbow from the block's outlet to the pump intake. If so, I would rethink the loop so that isn't needed.
A system will have a sweet spot: too low and the waterblock's performance is compromised, but too high and radiator performance typically suffers. I wouldn't think an Eheim 1250 would add enough heat to make any difference; air in the rad certainly would though.
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