To start I would like to let you know that I am not a expert. I just like to grow aquatic plants. One of my favorite plants are sword plants. All I can do is relate to you my experience in raising them. I keep my tanks around 6.8 - 7.2 PH and KH 4-5. I try to keep NO3 at 5 - 10 ppm. PO4 .2 - .5 ppm. I try to keep a 1 to 10 ratio 1/10 PO4/NO3 this seems to keep algae under control.

First lets talk in general.
Swords are beautiful plant but most of them will out grow their tanks. I see allot of post wanting to know how to grow sword plants so first lets talk growing. They need lots of ferts at the roots, and a good source of potassium. In gravel substrate I use a 13-4-5 plant stick cut into thirds. Put two to three around the roots along with Iron root tabs. Remember that if you use this method leave the plants alone. To get a growth of two to three leaves per week the plant needs to be stable, You don't want to disturb the root tabs, that could cause algae blooms. In Eco-Complete substrate you don't have to add any tabs. These are the only two types of substrate I have experience with.

I have seen some post about sword melt down. I've had this problem early on in my attempts at raising swords. The leaves would just melt in hours. You could watch them melt that's how fast it can happen. Root tabs alone will not solve this problem. I tried just about every thing but I think what plays a roll in it is very low potassium levels. After increasing potassium and maintaining it the problem went away.

Light? You need at lest 2w/gal, 3w/gal is better for faster growth. I have never had any thing over 3.5w/gal so I can't comment on very high light. CO2 is helpful for faster growth. I have raised Amazon Swords in tanks without CO2 but the tanks had high NO3 levels. It was hard to maintain the high NO3 levels for long periods, algae is hard to control at those levels. That is why you need to use root tabs. You can feed NO3 at higher levels without algae problems.