I agree with those who are recommending a bulb change...
I also would question your photo period as being an issue. In nature, plants (and fish for that matter) don't receive light in broken periods throughout the day. You should find 7-8 hours a day straight to run your lighting. If the plants are healthy and photosynthesizing properly they should help a bit with the Nitrate issue as well.
I would also recommend relaxing on the vacuuming a bit. Constantly churning up all of the bacteria stored in your substrate as well as all of the other junk in there is basically making it easy for bacteria to thrive and making it hard on your fish, as well as to a lesser extent your plants. I'd say only lightly vacuum the top of your substrate (don't suck any substrate up into the tube) Especially with a sandy substrate like it looks like you have. And maybe only do this a couple of times a month.
Also if you only have a couple of root feeding plants, you shouldn't need a lot of root tab ferts. Your water column ferts are more important for the others.
Other than that do a big cleaning of the glass and 50% water change twice a week until the issue improves then resume a weekly program with a light vacuum, glass scrubbing and 50% water change.