Why do tanks crash?

[abcha0s]

I've had a couple of misfortunate happenings.

My last fresh water tank was shut down due to a heater malfunction. The heater stuck on and cooked the tank. While the loss was sad, this sent me looking for an aquarium controller which lead me down the salt path.

I had two flame wrasses die in my 90G from what I believe was shipping stress. (A good argument for QT). The problem was I couldn't get the dead fish out. The water quickly went bad. With a series of massive water changes and the careful use of Prime, I lost only my shrimp and brittle star. The rest of the tank survived but it was a very close call.

I had another near miss when my Tunze ATO pump decided to stop working while on vacation. The return chamber in the sump ran dry and the return pump ceased. The real problems started when the tank sitter found the problem. After replacing the return pump and restarting the ATO pump, the ATO proceeded to pump 5 gallons of Kalk saturated water (pH 12.4) into the tank. The pH in the tank quickly rose to over 11.

Heres where the controller saved me. I received an alert for high pH and figured out what had happened. The tank sitter returned to my home and slowly brought the pH back down with vinegar. No losses. Thanks Bryce.

My new tank has two controllers, two return pumps, two groups of heaters, two fans, two ATOs, two auto feeders, and two skimmers. All of the critical equipment is split across two separate electrical circuits. Each controller manages one set of the listed eauipment. I'd still say there are potential problems, but I've gone a long way towards reducing risk.

I asked the question just for fun and to see what other peoples experiences have been. I'm very happy to learn from other peoples mistakes - especially if it saves my tank. Anyways, the chiller poll had been up for long enough.