1. 1974 buying a whale fish & placing in 15gal tank w/ red tiger oscar!
2. 1984 buying 20 variety of my favorite fishes (all small size) at great low prices on biz trip in LA, travelled another 4days to SF/Chi then home to NY. kept in plastic bags re-aerating them daily. they traveled well. but time I got them into my 20gal tank 8 doa!
3. 1986 love discus - had 20gal tank but kept buying n buying. ended up with 12 nice sm-med size (back in the early 80's when they cost only $10ea.) - needless to say they developed fin rot & slowly died one by one - finicky peckers!
4. 1973 silver angels bred but didn't know how to save the fry
5. 2009 latest no-no was earlier this yr, re-started hobby after 20+yr layoff, went to petsmart, bought 20gal tank starter set, 4 baby silver$, 1 baby redtail shark, 1 baby rainbow shark, 1 med albino shark, 1 baby bala, 4 baby albino cory, 1 sm algae eater, 2 med bloodfins & water conditioner/de-chlorinator. of course this goes against all the rules, but to my surprise (& hopes) they all survived for a good 2weeks w/ no casualties, but 1 cory died of aneurism in the belly, rainbow shark cuz it was dominated by redtail & algae eater cuz not enough to eat. to date, silver$ are 3x's their baby size, bala doubled in size, no more sharks, 2 albino cory are big & fat/3rd medium size, bloodfins big n fat, added baby bala, a betta & a pleco. all doing great.