Soil pH and acid

A bottle of sulphuric acid. This is a lead acid battery refill pack, 37%
The lab is ready, advanced as it is. I love those measuring spoons, they're my mums, I'll have them until I die. They're funky 60's orange plastic. The acid is far to strong to neutralize the sample with accurately. Here, I'm diluting a 3ml spoonful down into a 2l bottle of water

Acid in and rinsed in from the spoon and funnel, I've 1/4 filled the bottle with water and given it a shake. If I filled it to the brim and then shook, I'd be encouraging it to not homogenize

Stock solution of acid. This is so dilute I can drink it and only just taste the acid

I'm using a glass jug to dispense the acidic solution. Not because it'll eat anything else, but because the scales won't weigh the 2kg the full bottle weighs. I need to weigh the jug as I add the acid so I know how much I'm adding, then I'll be able to work out how much acid has gone into the sample and so know how much base it's neutralizing. This is a standard chemistry process called titration

The pH meter doing it's magic. I have to routinely stir the soil to make sure all the sludge on the bottom gets neutalized

6.5 is about where I need it to be. But, unlike the terrible garden centre dye kits, my meter is climbing a .001 or .01 every second at the moment, and so I know that the amount of acid I've added so far isn't enough. The climbing indicates that the acid is still neutralizing base. Anyone familiar with hydroponics will know what that means. It means that if I leave if for a while and come back later it'll have risen back towards neutral, away from the slightly acidic I need. The acid is not being 'washed out' because it has no where to be washed out to from this sealed container

A bath later and you can see what I'm talking about, it's already risen another .3 pH points. That's not a temporary change, it's that the acid I initially read in the solution has reacted with the base. Basically, I need more acid