I'm having problems with my aquarium plants!!!

Hello guys. Recently I took my friend's aquarium because he is going out of the US and I offered to take care. I don't know what he did and what kind of fertilizer or other stuff he used, but I do not like what I am seeing. The plants are not as they were supposed to be, and I have never seen something like this. Personally, I use fertilizers I buy on Amazon, Green Leaf Aquarium, and NilocG. The last one is the most used one by me, and my other two tanks are looking great. Now, this tank is a freshwater one, and I do not know if I am supposed to use any aquatic plant product at this point or change all the tank's setup. I am attaching some pictures, hopefully, they are clear pics that I took the moment I received the tank. Don't worry about the fish, they are moved to another tank, a smaller one, temporarily.

Did anyone of you have this same problem? How did you resolve this? Do you suggest me investing in improving this actual setup, or maybe changing it completely? What is the most logical, less time-consuming, cost-effective solution?

If the pics are not very visible, note that the rocks are turned black and the plants, brown shade! Also, the pressure of the switching pump was not proper, and I changed it. I know that this does impact, but I am not sure about the fertilizer stuff.

Thank you in advance!

first fill the tank up, more swimming space.
look in the drawers and whatnot to find root tabs, small tabs that are usually dark gray/green and look like vitamin c tabs, smells like a generic "rust" pop some in in the middle of a group of plants, 3+inch apart
if you have a plant that looks like this (anubias species)
grab it by the leaves and pull it out of the substrate if the part where the stems of the leaves grow out of is under the substrate


that's my opinion, those stringy plant(valisneria idk how to spell it XD) look like they need some root tabs

the image did not seem to upload
it is in the attatchments