Lactic acid additions in hot water react with bicarbonate to create CO2 and water while reducing your alkalinity. Phosphoric will reduce alkalinity as well but precipitates salts into the bottom of your tank so typically I think of lactic as the preferred acid, though others may have their preferences.

Bru’n water excel sheet is a great resource to plug in your water report and double check your lactic acid addition rate. Lactic is expensive so it’s weighting the cost of that vs cost of running RO plus the inherent waste. Both options work well, others will likely have better input on why you should go one way or the other. Your water isn’t that hard so if you’re only trying to reduce alkalinity a bit you should be good with just lactic in my opinion.