Hi mate, adding a teaspoon of agricultural gypsum to a litre/quart of water will help stabilise your ph in soil. I use it for the same reason just to give my plants a boost of calcium in flowering stage. At the same time it helps keep the soil stabilised. I hope this helps, good luck and happy growing
If it's close to range it's likely ok. If your soil is way out of wack, you can make it less alkaline by adding Sphagnum Peat Moss, elemental sulfur, aluminum sulfate, iron sulfate, acidifying nitrogen, or organic mulches.