I kept tropical fish about 20 years a go and I stopped buying guppies for this reason ! they were notorious for perishing very quickly and very dificult to keep beyond about two months, they were also prone from attacks from other fish, pretty fish but not very hardy !! It takes time for the good bacteria to build up in your tank, usually a good 2 months at least and when cleanining the tank only remove a third to half of the water and about every month, you only have a small number of fish so will not require very frequent cleans. I used a pump sucker thing to remove the turds from the gravel and a magnet cleaner for the sides.
I had a 5 year stint at this game. As the family kept calling me the fish murderer then I don't think my advice is what you are after...I really really tried too but gave the lot away in the end...prob about £500 worth...
I've had tropical for a couple of years now, started off with 6 minnows as they were supposed to be hardy, 5 of which died over the space of a couple of months. Bought 6 harlequins, again 5 died. The remaining singles of both are still fine 2 years on.
Had various other odd ones - gourami, betta which lasted a while but died and had some guppies, again they died over a few months. Now have about 20 guppies, a pleck and something I can't remember the name of lol. Apart from one guppy which looked like he'd been fighting haven't had any die for 6 months+ had a bunch of babies which have all survived - or been eaten as no remains!
It does take time for the tank to settle down, be careful not to overfeed them, and your ratio of male - female is off as the males will harass the females too much.
Just the fact that some geniuses were laughed at does not imply that all who are laughed at are geniuses. They laughed at Columbus, they laughed at Fulton, they laughed at the Wright brothers. But they also laughed at Bozo the Clown.