A little experiment and a couple of things i noticed.

I tried making my own acidic mix of food for my plants, i havent used it yet, and dont know if i will. But while doing it i noticed something about acids.

I used coffee grounds and tomatoes.

I blended about 2 cup fulls of coffee grounds (used), with two whole tomatoes, and a cup of warm water (my tap water ph is typically between 7.5-8.0.

After blending it all the Ph in the mix went down to 5.0, which is quite acidic. I put it on the shelf and came back an hour later, the liquid got to room temp, about 60f. At this temp the ph was back up to 6.5. Still more acidic than the water on its own but not as alkaline as the water on its own. SO i warmed it up again in the microwave, and the ph went back down to 5.0.

What i noticed was the colder acids are the higher they become in ph, ie more alkaline.

Probably something everyone knows but i thought it was quite interesting. I have since put heat pads under my plants in hopes this will naturally bring my soil ph down.

Can someone tell me if it would be ok to add the mix i made to my plant food?

I believe when you heat water you are disturbing the H20 molecular lattice and by increasing the heat of a liquid its molecules move faster. So the pH you are reading is dependant upon how much you have heated it, or let it cool for that matter. Your pH should be read at room temp/grow room temp. I would think it would be a messy hassle to keep creating this coffee/ tomatoe mixture. I only have to adjust my pH down, and when I do, I use a couple of capfulls of acetic acid (White vinegar).