hey i have had a tank running for about.... 1-2 months after my previous fish died (tiger barbs).... i water changed it than thinking maybe i should wait for the nitrogen cycle to take place. than for maybe 3 weeks algae started to form on the glass so i changed the water again... than 2 days before i got my new fish (3 Guppy's) i changed the water about 60%. i didn't really put food or anything in the tank to cycle it between the 2 months... maybe a pinch every 3-4 weeks... well anyways 2 of the guppies died within 5 hours...
what are some possibilities

when i first put in the guppies.... 1 went completely berserk and was swimming rapidly crashing into things before passing on, on the bottom. the one remaining guppy looks perfectly fine... for now...