What were your biggest purchase mistakes?

[whatcaneyedo]

This looks like a fun game!

Coralife PC fixtures. I've had two 65W ballasts burn out within a year for no reason.
Coralife Aquagloves. I've bought two sets and within a year three out of the four gloves leaked through the seams.
Coralife timer powerbar (anyone see a pattern here?). The little sliding covers broke very easily and the timer would occasionally not shut off the lights!
AquaMedic Biotherm Controller. They don't even make these anymore... Two of them lost their their calibration within two years and cannot be re-calibrated. What good is a temperature controller that is out 8ºC?
AquaMedic Titanium heaters. I bought three and had to send three back when they would no longer heat up. All within a year.
RedSea Prizm Skimmer. Needs no explanation.