It's low tech for now.
I also have a 55 gallon that I have as a community tank. This is the tank I am having issues with. I'm using aqueon led lights (2 18 inch lights I plan on upgrading to something more powerful in the future I know these aren't the best). I have been using flourish by seachem (I also know I need to add macros on top of that that's why I'm here). My lfs only has seachem products which I would need at least 3 different products to get the full amount of nutrients my plants need to grow fast or tropica which is safe for fish but as far as invertebrates I don't know for sure and I want to make sure it's okay before I buy. It looks like it's very similar to thrive based on the websites description but the shop I go to doesn't have it maybe it's not available in Canada? Or if it is maybe someone can direct me to a chain that carries it. Thanks!
OK, a few observations here (on the 55g, low tech).
Seachem's Flourish Comprehensive Supplement is as the name implies, just a supplement. It is primarily intended for low-tech or natural planted tanks with moderate light and no added CO2. It contains all the necessary nutrients except oxygen, hydrogen and carbon, and the nutrients are balanced. This is important to keep in mind, because too much of some nutrients can cause deficiencies of other nutrients or other problems for plants. I have been using this product now for ten years. It takes very little as supplement to fish foods and water changes. And that is where your macros come in; it should not be necessary to add them, nor is it wise. Depending upon the fish load, and the GH of your source water, Flourish Comp may/should be sufficient. Used according to directions, it is safe for invertebrates. But overdosing could cause issues for these, and fish, as well as plants, and lead to problem algae. In most tanks this is probably all that will be needed.
Depending upon your GH, the hard minerals may be insufficient. I have this issue, with my zero GH water. But as I keep very soft water fish, mostly wild caught, I am not adding anything to increase GH, so I found the Flourish Tabs worked. These do not release nutrients into the water column except in the substrate where the plant roots take them up, so the fish are safe.
Second, your issues may be light related. Light drives photosynthesis, and each plant species has its own requirement when it comes to light intensity to do this. And, there must be red and blue light, with more red, to achieve it. Green in the mix has shown to produce the best results, probably because of the increased intensity and similarity to sunlight which is strong in these three. Without sufficient light (intensity and spectrum) the fertilizers will likely result in algae.
Third, plant additives should always be minimal if fish are present. Not only can the plants be negatively impacted, but the fish are. Every substance in the water gets inside the fish, into the bloodstream and internal organs. "Safe for fish" cannot be taken literally.
I live in Vancouver and to my knowledge no store here carries Tropica, so it may need to be ordered online. But having not used it, I cannot comment on its effectiveness or safety.
