There has been a lot of good stuff said since I last tried to contribute. I think you have some problems to sort. Air bubbles are okay - powerheads that move water are better but you have fancy type guppies and they swim badly.
I'm like a lonely hermit in the hoibby, in that I will never allow a black skirt tetra group near my tanks again. I was delighted when they became rare in the hobby, and unhappy when they were used for the genetic splicing that created glo-fish. That brought the fish back into the hobby. They intimidate smaller tankmates, sometimes nip them, and don't look or act interestingly enough to worth the disruption they cause.They are easy to breed and dirt cheap for stores, so they are usually on offer. There are so many better tetras. Would I suspect them of harassing or simply stressing often fragile fancy guppies? You bet.
Rant over.
I can't comment on the loaches. If they're a mistake, they are one I haven't made.
It seems possible to me that the platy and sword were just unrelated deaths of fish recently put in the tank. A lot of big tailed guppies are delicate. A species that was once very hard to kill can now be very hard to keep alive, if you get a batch from a bad source. Stores search for good sources, but guppies have suffered from chains driving prices and quality down. You could be working hard to remedy a situation that has nothing to do with your tank - a batch of poorly raised guppies with a predisposition to a short life.
The UK chains I have seen are better than the US ones by leaps and bounds, but the entire international fish farming market is affected by a few mega-buyers, so things happen.
I'm like a lonely hermit in the hoibby, in that I will never allow a black skirt tetra group near my tanks again. I was delighted when they became rare in the hobby, and unhappy when they were used for the genetic splicing that created glo-fish. That brought the fish back into the hobby. They intimidate smaller tankmates, sometimes nip them, and don't look or act interestingly enough to worth the disruption they cause.They are easy to breed and dirt cheap for stores, so they are usually on offer. There are so many better tetras. Would I suspect them of harassing or simply stressing often fragile fancy guppies? You bet.
Rant over.
I can't comment on the loaches. If they're a mistake, they are one I haven't made.
It seems possible to me that the platy and sword were just unrelated deaths of fish recently put in the tank. A lot of big tailed guppies are delicate. A species that was once very hard to kill can now be very hard to keep alive, if you get a batch from a bad source. Stores search for good sources, but guppies have suffered from chains driving prices and quality down. You could be working hard to remedy a situation that has nothing to do with your tank - a batch of poorly raised guppies with a predisposition to a short life.
The UK chains I have seen are better than the US ones by leaps and bounds, but the entire international fish farming market is affected by a few mega-buyers, so things happen.