Well, 12 hours is too long. Try ~7 hours, use a timer. You can even split the time if that works for your tank viewing schedule. I haven't gone to LEDs yet so have no opinion on yours.
As for ferts, you need to test & see if you need to add them. A nitrate level between 5 & 20ppm (max). Also GH & KH tests can help. Test your tap water too. Most of us here on AC use API Master Freshwater kit. It looks like your other plants are sword plants? Those are primarily root feeders & would like a root tab fertilizer every 3 months. You should be in the habit of changing 30-50% water every week or so.
The top 1-3 inches of your stem plants look healthy. Let them get a few inches longer. Then you'll want to prune off the pretty tops, uproot & compost the ugly bottom parts & replant the tops. It depends on how fast they grow for you & how ugly the bottoms get as to how often you might need to do that. If you don't have naked stems or unhealthy leaves you can let them grow as long as you want.