It is extremely unlikely that you really have 25 ppm if you just measured the tank KH and pH. You need a drop checker, with known KH, otherwise pure water in it if you want to know how much CO2 you really have in the tank.
I seriously doubt it's because of the light unless you have it mounted really high off the tank of you have shaded spots on the outskirts of the tank and that's where you decided to plant.
I have 192w of pc on my 30g, 30-40ppm co2 with lots of fish and double the EI rec. for the tank and I trim about everyweek. But like the others say I have lots of stems that would grow fast under the right conditions, I also have HC spreading like wildfire!