What type of filtration are you using? Just normal cannister filtration? My plants grow extremely well with out the use of fertilizers, or other stuff. I dose occaisionally, nitrogen, iron, phosphorus and some other trace elements. As well as some bacteria every water change. IMO lighting is the best way to get optimal plant growth. IMO, and its my opinion only, that your issues are coming from over cleaning your cannister filter and removing beneficial bacteria. I did the same thing as you when I started freshies and my tank crashed twice. IMO you only need to clean out your cannisters once every 3 months minimum. As otherwise you are taking away to much of the bacterial goodness. My cannister filter even houses cherry shrimp that get sucked up all the time and I put them back in the tank every few months I clean it out. They live happy in there with no problems. I would suggest cutting back your maintenance routine of the filtration. And go back to 10% a week water change. I think that is ample for fresh water.