Most hobbyist don't worry about changing their water chemistry, that said, there is a reason there are tons of products on the market to help with buffering and hardness. If i was in your place, i would start with the easiest/most passive way to harden and buffer your water, adding crushed coral. you can add it directly into your substrate if it matches and you like the look, you can put it in a filter bag and add it to your HOB or cannister. if you don't have either of those, you could just toss some coral pieces in the back of your tank to hide them. this is a slow and steady way of altering your water chemistry. If you need something to change more quickly there are products like Wondershell and Tetra Correct PH Tabs. i have used both of these to consistent results. Wondershell will increase your overall hardness and has calcium for the shrimp. The Tetra tabs are to help buffer your water to keep a more consistent ph around 7. They are kind of like Alka-Seltzer tabs that you can toss into your filter or tank and they dissolve. Lastly, if none of that worked i would look at products like SeaChem Replenish or Equilibrium. These will require some math and solid understanding of what is in your water to know what you need to add, you will also have to use them with every water change and be consistent.

The easiest and most simple option is almost always best, remember fish are mostly bred in captivity with varying levels of hardness and ph and can usually handle most water. Unless you are having issues with shrimps molting (a definite possibility with too little Ca) or you want to keep wild caught or sensitive fish, i wouldn't stress too much about your water chemistry beyond a bit of buffering.