What were your biggest purchase mistakes?

[VFX]

Biggest mistake is my 1st tank when I was in my early teens.

That set the snowball rolling that has so far led to a 6x2.5x2 currently sitting in my basement & a 72g in my living room.

Lord knows how much it's cost me in terms of time, money, blood, tears & probably relationships!

But in the spirit of the thread, biggest mistake so far is a Via Aqua skimmer, UV filter, heater all-in-one HOB thingy. That thing was louder than a 747 on take off & pulled as much cr@p out as broken down Red Sea Prism. At least I never had ich with that UV going.

Best part was parting somewhere around $500 for it