light drives the plants
Because light drives the plants, causing them to require more nutrients (N, P, K, , traces and Carbon) you have to give them that or else they will fail in one way or another.
I had a 20H with 55 watts and very low input of DIY CO2 via a gelatine mix and it was fine. It was also very overstocked with fish and I worried about it a lot when power went out or the tank temp got high. The same tank with 36 watts would have been less of a concern and probably would have been fine with Excell and no CO2.
But, you can lower the lighting by adding driftwood that stains the water, by letting the glass get dirty with water splashes, by raising the light up a bit to increase distance. Or replacing the bulb, for many ballasts can run 55 or 36 watts (but check with someone who knows for sure!)