Yesterday evening I could not wait longer. At midnight I needed about 40l of water to close the loop. That takes about 2 hours to make, so I decided to go to bed instead.
This morning I filled the remaining water and voila - everything worked. No leaks (touch wood). However my durso standpipe was not working. Water was oscillating up and down vigorously. I decided to remove the top and cut off a 4cm piece to lower it (it was too high). Since I dread leaks I cut it in place - and did not remove the pipe from the overflow.
Once cut, I placed the durso head back but no luck - same thing.
I read that the reason for this is back pressure in the pipe. Since my pipe work does not descend below the surface of the sump water level, the only other explanation I could find was that my pipes are not sloping enough. They are not horizontal, but they are close (maybe 2 degree slope?). Since there is NO WAY I am redoing all that cutting and gluing, I decided to remove the one 90 degree elbow from the standpipe's head. It now only makes one 90 degree bend where it sucks in the water. The cool thing is that it is perfectly quiet and it is not oscillating anymore.
The main return pump is a bit loud (Haelia), but I hope the noise will subside a bit as the biofilms starts to grow.
The chiller has a heat mode, so currently I am trying to raise 2000l of water @ 14C to 25C with the chiller and one 300W Jager heater. Once I reached the desired temperature, I am going to add salt... If it breaks this time I'll personally drown some people in the flood water...
Back to work.