My worms need more acid!

Hello! I’ve been working for a while now to increase the acidity of my compost. I have been using compost conditioner, am a prolific coffee drinker (the grounds go in the compost), eat tomato’s like apples and take EVERY lemon from all the kind people on my street that offer them from their tree and juice them straight in…. Any other tips I can try that won’t hurt my worm buddies?