I have a 55 watt power compact 8700k over a 29 gallon tank.
Try pair of 20W T12 or go with a 40Watt PC light(A&H asupply sells them, they work in all ballast that drive a 55W), then bend the reflector outward to give you more spread, if you can raise the light a bit, that will also help.
In the meantime, try using metal screen, maybe 2-3 layers worth to block some of the light, it's a bit intense for what you want to do.
Non CO2 typically entails not doing water changes, so fish loads should be balanced reasonably and plant biomass should be high. Floating plants like water sprite are another option, blocks the light, mops up the nutrients, and gets CO2 from the air, plus it's sitting right under the most intense light.
If you want to go to CO2, then you have more options, plants want CO2, not some pH. That's why we add CO2, to make plants grow better, faster, richer, and also to hep other plants that cannot compete well for CO2 or use KH as a carbon source.
Many add lots of light then get algae without balancing CO2/ferts.
Better to add just enough light, then CO2/ferts are much easier, less algae etc.
Regards,
Tom Barr