dying plants

I want to help out my dying plants. I recently switched out my gravel substrate to sand. I wanted dirt instead but was told that cories need sand. I'm new to keeping live plants and there's only one product near me that says plant fertilizer. The other products help in different ways. There are...

Hi everyone, do you know what would make my plants die like this? It only happens with these kinds of leaves thanks!

I am new to plants , my experience in plants is turning my Marimo moss balls over ever week , about a month ago I buy some Amazon swords as I herd they are easy to grow and are very much for lazy plant keepers , but they seem to be dying , my tank is set at 26-27c is it too warm for them? They...