The 12K bulbs are not "wrong spectrum". And the 6.7K are not "correct spectrum" either. The Kelvin just tells you approximately how blue or red the light appears to you. The plants "see" it completely different. Also the manufacturers of the builbs like to just slap a Kelvin ratings on their bulbs without being very precise. So a 8K bulb may appear whiter than a 10K bulb. Go figure.
Overall don't get too worried about which bulbs to leave on. They all work for growing aquatic plants. Some bulbs are better or much better, but you can grow plants with practically any white (reddish, white, or bluish) light bulb you can buy.
The best results (least algae) consistently come from using a midday "burst" of strong light lasting 1-6 hours. The rest of the time (before and after the "burst") you just leave "observation" light - low light that does not allow algae to grow but allows you to see the tank well.
I'd suggest having 2 bulbs on 9 hours a day. And 6 bulbs on for 1 hour a day around noon. Start from that and see how the plants like it. Noone can tell you what they will like so just observe them.
--Nikolay