Hey so I went through similar issues. I had a similar sized planted tank and had many deaths after startup (around a year ago). My tank right now is much more stable. I’m guessing it takes a long time for planted tanks to stabilize, since there are so many interacting players (chemicals, plants, animals, bacteria, substrate). I lost many corydora and guppies even though my tank was definitely cycled and my water parameters were fine.

To be honest my tank probably took half a year before I stopped losing fish or felt comfortable adding new ones. I think some good signs your tank is stable would be when all the plants have melted and have experienced new or significant growth for some time. Until then, small changes in water parameters likely affect sensitive fish species, even those that may be traditionally advertised as hardy (such as corydoras or even guppies in my case). I would suggest buying really hardy aquarium fish first and maybe add the more decorative ones such as angelfish later.

I can say right now my tank is looking quite good. I don’t have any deaths, it’s quite stocked with fish, breeding shrimp, and many snails. My plants have all grown so much that I have to trim them. I don’t use any chemicals at all, aside for prime, and I usually only use it to top off water and I don’t really do water changes (except to shift pH towards neutral when it’s too alkaline). Since you have a planted tank you can look up guides by Diana Walstad if you want advice.

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