I keep a small FW planted tank but are by no means an expert. My tips however are:
A) Do not use phosphate based buffers. Ever. If you want to use a buffer use a Calcium Carbonate based one.
B) Put crushed coral or shells in your filter. This will help increase Kh and add minerals etc to your tank that your plants will benefit from. It will also act as a buffer as one thing you are effectively adding is Calcium Carbonate.
C) Keep up your water changes to maintain Nitrates < 40 ppm.
D) Have good biological filtration.
In my case I have a power head lifting water into a top mounted trickle filter. It comes with two filter pads, so I took out the right one and replaced it with ceramic noodles and shells.
It is also quite safe to add small amounts of algicide to assist but only after you get the basics working well.
Here is my FW tank.