I was quite happy with how the system ran. Very quiet and no issues save for this one minor one.
Yes, that is a small leak from that fitting. I guess there wasn't enough teflon. Instead of reapplying it I ended up siliconing all the threaded barbed fittings just to be on the safe side. In order to do that though I had to shut the system down and take those barbed adapters out and dry them. A great opportunity to do a power failure test!
This is what the sump looks like after a powerfail and the water has drained back into the sump.
There was definite lack of flood water on the floor which everyone in the house appreciated. The water in the main tank only drained down as far as the bottom edge of the overflow weir. To break the siphon from the returns, these holes were drilled into the sides of the return nozzles which are at the same level as the bottom edge of overflow. In normal operation the water rises above these holes by about a half an inch. This prevents air from being sucked into the return line and shooting bubbles into the tank.
So now I wait for the silicone to dry and power it up again tomorrow. If all goes well I will flush the tank and sump and fill it with salt water instead of that nasty tap water.