20g Tank
5 Painted Platy
3 Bloodfin Tetra
0 Ammonia
0 Nitrite
5-10 Nitrate
7.2pH
All Using API Master Test Kit

I have a fish die nearly once a week and I'm frustrated beyond all belief. I very briefly (2 days or so) had an ammonia reading of 0.25 (1 fish died) when I didn't do my weekly 20% water change. To reduce the ammonia, I skipped a day of feeding and retested the water. 0 ammonia. However, 1 more fish died.

Are they that sensitive?

Even though it said 0 ammonia, 0 nitrite, and 10 nitrate, I went ahead and did my usual 20% water change today. Some of these fish sit at the bottom of the tank quite a bit or hide in a little cave. I read that bottom-sitting is a common sign of ammonia toxicity, but how is that the case if it reads 0 ammonia?

I'm incredibly annoyed and about to throw in the towel on the whole hobby. I've been trying for over a year at this point and while I've learned a ton, I killed a fair amount of tiger barbs over a year ago due to not knowing what cycling was. Having grasped the cycling process and watching HOURS of YouTube videos, I was confident in this tank.

2 weeks in and only 1 fish had died. The pet store said sometimes just the transfer of them stresses them enough to kill them so I didn't think anything of it. Now after having the tank cycled and stocked for over 2 months, I've lost 5 fish in total.

My dream of having a 75g barb tank and an even bigger cichlid tank are just about dashed.