Went away for 2 weeks to Akaroa.
Two days before we left I heard a funny noise coming from the tank in the morning.
Got up to check and to my horror the display tank was overflowing!
Quickly turned off the return pump and the auto-topup, grabbed towels and mopped up before my wife got up! Luckily, it had failed not too earlier and 'only' dumped about 30 litres onto the carpet!
A bubble in the overflow was the cause due to me having dialled down the flow too much I think.
I couldn't find my instructions to restart the flow so gave up until I could devote time to it after my holiday.
Jury rigged a solution using my auto-topup to pump water from my sump to the DT, and moved the autodoser to above the tank and the hoses directly into the DT. This was going to increase the Ca and Alk and the salinity but I wasn't too concerned. Also with my skimmer in the sump I was going to see an increase in Nitrates.
Tested my water today before doing a water change and results were:
Ca 465
Alk 11.5
Salinity 1.028
Mg 1365
Nitrates 1.0
Just did a decent water change, removed my tank cover and fixed the overflow and increased the flow. Everything all back in its right location now and working fine.
One thing that I've considered is how lucky I was that my power cables are over the ground and have slack so the water cannot flow to the wall Power point.
I think I'll investigate a solution so the return pump cannot overfill the DT again.