I'd like to offer a few suggestions of a general nature to help you.
First point to make is...never, absolutely never, assume anything you see on the internet is correct. Unfortunately, there is frankly more inaccurate advice than accurate on sites like YouTube (when it comes to this hobby). Unless you know the individual who posts the "advice"--and by "know" I do not mean personally but that you know the individual has the credentials/knowledge behind what they say--ignore it. Find the individuals who are the true "experts" and forget the rest. I know how daunting this can be, but it is a sad fact of the way things are today. When I entered this hobby more than 40 years ago, there was no internet, and we had books and the cost of publishing meant that the vast majority of them were at least reliable. The reliable individuals on the internet are there, but you need to know who they are. Advice from the members on this forum can help with this, as many of us have gone through the same problems, or have learned who is and who is not knowledgeable. Experience in this hobby means nothing if the person with the experience does not also have the necessary knowledge.
Second important point is...no one, including you, can ever say their fish are fine, or "perfect." We cannot talk to the fish, and regardless of what anyone else says, without being able to any assumption that all is well is just that...an assumption. If any one of us provides all that a fish species requires--and to determine this we research the species and the habitat environment from reliable sources--then we can intelligently assume the fish is "fine." But not otherwise. Read the two important citations in my signature block, please.
Third, just as an aside...as mentioned by others, ammonia and nitrite need to be zero, and nitrates need to be as low as possible and remain there. IF nitrate increases after one water change until the next, something is wrong biologically. You may need to do more frequent or larger volume water changes, or vacuum the substrate (plecos are very messy fish when it comes to waste and its effect on the biological system), or clean the filter more, or reduce the amount you feed the fish, or consider if the tank is overstocked. All of these can increase nitrate. Having live plants, even if just some good floating species, makes a big difference as they take up considerable ammonia/ammonium and this means the nitrates will be less and more likely to stay less.
Don't be ready to add "mdicines" to a tank with fish. Clean water is far more helpful.