You can add a sprinkle of garden lime on the surface of the soil and it will slightly adjust the liquid poured through it. When testing runoff pH, be sure to test the last few drops that drip out after watering. Samples taken closer to when the plant was watered will show less of the soil pH and more of the original liquid's pH. An even better reading can sometimes be had from pressing on the soil the day after a good watering and collecting the runoff. This way the liquid has 24hrs for its pH to equalize with that of the substrate.
Nitrogen deficiency looks to be more of a problem than the pH anyway, so this is just discussing a secondary issue, mostly to keep it from getting worse.