Leaves are no longer dark green. Any ideas?

It's good to remember that plants look paler under grow lights than they are in reality. However, if it's trending in that direction, it still means you should react to it and adjust your fertilization formula accordingly. You might be locking things out with too much P. This would cause chlorosis in new growth and interfere with K which causes the damage around the serated tips. Even though you have reduced fertilization lately, your ferts look like the type that slow-release due to need for microbes to break them down... so even though you reduced what you are adding to the soil, there's a buildup prior of 'inventory' for microbes to work on and continue to provide plant-available nutes around the roots. with soil and your fertilization methods, it'll take some guessing and trial and error. E.g. this time i'd take note of when you started to reduce and maybe do that 1 week sooner. or take 10% off what you fed each cweek prior etc... some sort of adjustment that adds up to a bit less concentration in the substrate by this point in the grow. in the end there is not enough infor to be confident. diagnosing from leaf symptoms alone is not 100% accurate. Symptoms are not discrete. pH and nute lockout are always possible too. the reason i didn't go with K-deficiency is that there is little to no interveinal chlorosis of mid and lower leaves. High P can cause issues with Ca too, which is potentially one of the symptoms seen too.