Well, as far as I know there are no tricks to getting your plants to thrive and come back, other than patience and awareness and understanding of a planted tank. Knowing how to tinker with the pH isn't going to help them any either. The key to understanding your plants starts with understanding your water and what the type of plants that you have require.
In order for us to help you and your friend with the plants, you need to provide more specifics about the tank.
IE how long has it been set up, what type of fish are in it, what's the substrate, is there additional co2, how many wpg from your lights, what kind of bulbs, what's the temp, what's the water params, what's the deal with all these whats?
The plants may not be thriving for a number of reasons and until you give us the specs, there won't be any way to find a solution.
Let's start with figuring out the what's of the tank, plants, water, and overall setup then go from there. Even the water paramaters out of your tap are vital