Nice looking tank. The OM should generate some nice random water movement.
I would consider using some hot water or a torch to heat the fibre re-enforced plastic tubing on your drain - that tubing, while clamped, looks too close to the end of that barb fitting for my liking (specially in the absence of a 90 degree elbow). Better still, consider using all PVC until you direct the flow downwards.
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I'm out. 
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