Fish Deaths

Help! My fish are dying. They look healthy enough and behave as normal. Then they disappear. I think the shrimps eat the bodies. I introduced 2 new guppies amonth ago. 1 died. 1 still alive. I have then lost my apple snail, 1 Endler and my best guppy- 2 in the last week. The Endler swelled up and looked pregnant although it had been sold as a male and had male colouration but behaved normally and fed well like that for several weeks then disappeared. This was the only symptom any of my fish had.

I havea foam cover for my filter inlet so the shrimps don't get sucked up so the fish aren't in the filter. Even my quite large apple snail is just an empty shell now.

I havea 23L Fluval Edge that I have had stocked since November, previously quitestable after fishless cycling. (Yes, I know that this is a tank that divides opinion but I like it so please don't be mean about it)

Current stock - 1 guppy, 1 Endler, 2 orange shrimp 2 cherry shrimp and some other shrimp that appeared that are colourless and a bit transparent that I think came as stowaways with the orange shrimp,. It is planted with a mixture of live and fake plants . The live ones are thriving.

I also have a lot of tiny snails that have appeared recently.

My water stats are

NH3 =0

No2 =0

No3 =25mg/l

pH = 8

I do a 20% water change every 2 weeks and hoover the gravel when I change the water. I use an algae scraper every month to clean the glass. I have kept the filter materiel and not changed it (on the advice of my LFS, as if contains most of the bacteria but I do rinse it in dirty tank water every month to get the big bits out.)

I am new to fish keeping and I don't want to be causing my fish to suffer through my own ignorance so please tell me if I am doing something wrong and how do I preserve the remaining fish and shrimp.

Thanks for any advice.
The photos are of the tank, my remaining guppy and a cherry shrimp with a small snail and one of the stowaway shrimp.

I can't see that you're doing anything terribly wrong. I'd be doing water changes twice as much (every week). From your description of the Endler, it sounds like it might have had a parasite or worms of some kind.

I've learned that the first thing to do is do a huge 80-90% water change. Then do another the next day. Just rinse out the filter media in the dirty water, just like you've been doing.

You're certainly not overstocked. Under, if anything. But of course I wouldn't get more fish until you can be sure the ones you still have will stay alive.