[somewhatshocked]

There's no one answer to "why are my fish dying" it depends on a myriad of variables.

Which is why you can't make blanket statements that all additives are bad, that tap water is "pish", that shrimp thrive on neglect, that dechlorinator kills fish, et al.

Anyone anywhere can enjoy an aquarium and have success if they keep it simple, local and stop watching videos of some rich kid somewhere

Many YouTubers do, indeed, create problems with newcomers to the hobby by creating unrealistic expectations. That's something a lot of us here and on other forums tend to preach. There are a few great YouTubers but many are just focused on numbers, ad revenue and metrics.

don't expect everyone all over the world to share that experience.

Which is why most people keep livestock that are adaptable to the parameters they have. Or they use RO/DI water to create ideal parameters and have dialed in control.

I never recommend commercial products because they become like drugs and the big companies are the dealers. If we can't do this without them they win. We don't need their permission to exist.
Be like water.

Great. But that's not what you said in your original post. Hence the need for elaboration.

There are plenty of ways to fertilize a planted tank and provide nutrients for plants. Not all of them rely upon large corporations. But using dry ferts purchased every 3-4 years from a fellow hobbyist is hardly like dealing drugs or becoming dependent upon something.

 

[Ticojon]

We've lost 50% of our guppy fish (4/8). Some within days and some weeks later after being transferred to the main tank; really sad. Meanwhile, in the same tanks, I haven't lost a single Harlequin Rasbora, Danio or Platy.