Yeah, don't change if things are going good now!
Of course that will change. It's always changing. :-)
Really EI is just a starting point (just like PPS). You need to adjust to the conditions in your tank. With EI it's typically down, although not always. And you have "complicated" things by adding plant tabs. Although in my opinion that's a good complication.
Not sure how you are measuring co2 but if you categorize it with a range of 15-20 I would hazard a guess that is limiting your nutrient uptake. While your lighting is high which is probably why you see changes in algae growth when you bump up Ferts.
Nice looking tank! And awesome that you found the sweet spot on light, co2, Ferts.
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