How can I change the pH level of water without using soda, baking soda, etc.?

It's for a science experiment involving plants. I don't mind if I have to buy a kit, but I would love if you posted a link to one.



And what levels of pH are considered toxic for life?



I need links that WORK. Thanks for the help people, sorry my question is so long lol.How can I change the pH level of water without using soda, baking soda, etc.?
the addition of any substance can change the pH of the water, tap water itself is normally around 6.5-6.7 not 7 like one might expect. It comes down to having a different definition of what an acid is and what a base is, there are effectively 3 different definitions, most people are familiar with the Arrhenius definition of increasing H and OH Ions but there are lewis acids/bases and bronsted/lowery (spelling is wrong) ones too, those fit most other chemicals based on likely hood of ';donating'; or ';accepting'; electrons.



Different things prefer different pH ranges I am sure you could find something to live in most pH ranges