You want something acidic to lower the pH, lemon juice or white vinegar for instance.

I would prefer to use proper hydroponics chemicals (pH Down) to do this, they are more stable and designed for this purpose.

Thanks for the info! I went ahead and ordered some PH down.

That's good. But you can buy some cheap battery acid, which is 33% sulphuric acid. Dilute that 1:10 (careful!!!!), and you get some very useful "pH-down" acid (3% sulphuric acid).
It will last you quite a while.

If it comes from batteries, it'll also probably be loaded with lead. Just order your chemicals from a chemical supply store if you want cheap, bulk supplies.

karenrei wrote:
If it comes from batteries, it'll also probably be loaded with lead

Not so. It's commercial grade sulfuric acid fresh from the manufacturer supplied in sealed bottles.

Then why did you call it "battery acid"? Why not just call it sulfuric acid?

sheesh. . .
you say toe may toe, he says toe ma toe...

In the shops where I buy it, they call it "battery acid". These people sell car parts, batteries, tires etc and most wouldn't know what you mean by "sulfuric acid".

So . . sorry for the confusion.

Hey, no problem :) I just assumed you meant you were literally draining batteries for the acid, and was a touch horrified by the thought. ;)