Greenish yellow is fine for now just keep an eye on your fish for any funny behavior.Not 100% sure how to starve nitrates since it's in ferts. But I did get a drop checker and also bumped up co2. I will increase lighting to 8 hours and go from there. The drop checker shows greenish yellow so about 40ppm I would say. A bit afraid to go any further in fear my fish won't like it.
If you did wan to try nitrate starvation you'd have to move to separate dosing instead of an all in one.
With the new photoperiod and CO2 tactics I would give it some time (long enough to see how new growth is responding) before you adjust anything else.
Small changes and see reaction instead of lots of big changes otherwise you have no idea what change actually worked.