Securing moss down onto a rock with a nylon hair net. Later on I found my female Ancistrus plec wrapped up in it. Had to cut her out using tweezers and scissors. She survived!
I'll never use a hair net again.
I don't know if it was my mistake or it was a malfunction in my equipment, but I've managed to explode a glass check valve!
I was trying a new diffusor and after connecting it to my nano CO2 system, I was of course eager to see how small bubbles it produced...
So I was holding the difussor in the tank with one hand and opening the valve with the other. Well, you know it's hard to finely adjust a valve with only one hand while staning in an awkward posisition, right? So i turned it up a bit too much and seconds later: BANG! That was the sound af my check valve transforming from a check valve to a lot of fast flying, sharp glass pieces. I even got hit in the eye with one of them. Nothing happened with my eye fortunately, but I was quite a shock.
On second thoughts... the Biggest mistake I've made was using DIY yeast Co2 mix, went to work came home to find the dog sleeping next to the bottle on its side and the tank full of Yeast and dead fish. Everything but the Clown Plec and the Corys died :/
I had a hydor eth boil a tank when it failed, I once dropped a rock mid re-space and shattered the base of the tank, once balanced a fresh macro mix on the rim of the tank only for it to fall in emptying everything in and killing all the tetras, gassed the tank a few times because of a shonky ebay regulator/needle valve. Many many things, using cheapo cotton that expanded in water and meant the moss fell off and got everywhere being probably the most long term frustrating.
Had a 400 litre tank break upstairs.Bought it from a LFS that was closing and had it set up on the landing upstairs and a couple of weeks later we were all watching TV when I heard a crack, thought 'what's that' then the sound of water hitting the floor above our heads.The carpet down the stairs had to be dumped, water came through the ceiling causing that to come down, wood floor in the front room lifted,leather suite soaked.I was not a popular puppy I can tell you with the good lady especially as the house insurance wouldn't pay as it wasn't ' fixed water feature' but at least the contents insurance did. Found out later the glass was far too thin but too late to get any satisfaction.Sometimes cheap doesn't work out cheap
forgot to plug heater back in for a week and lost pair of apistos.
put 'found' bogwood into tank and poisoned crayfish
attached co2 reactor wrong way round and cut filter pipes too short.
didnt check attachment to new lily pipe and emptied out tank overnight. had to replace carpet and underlay
brought a really cheap tank on a whim only to realise after that i would need to upgrade lights, filter, decor etc... not so cheap after all.