Hello! Sooo.... I have a few skulls to whiten, sanitize. I always used H2O2 30%. First time i had a bottle which had a very tiny hole to squeeze out the liquid. Next time i only could buy it in a bottle with big opening like the normal bottles, so it definitely gets contact with oxygene when opened. I wanted to use half of the peroxide and leave the rest in the bottle but after i closed the bottle back the bottle begun to heat up and i was afraid of it exploding so i had to use up all the peroxide. Now i bought online a 5 litre (1.3 gallon) h2o2 which i thought will have a bottle with tiny hole, but nope. It has a big opening and now i am not sure if i can just por out a little and close the bottle, leaving the rest for later use. Not sure if it is safe to close the bottle after opening it. Or should i delute it with water and store it that way. If so, i wonder how much water should i add to 5 litre/1.3 gallon h2o2 to dilute it so i can store it safely. Its basically impossible to find smaller volume H2O2 in big quantities in my country so i really can't go to the shop and pick the best one i see so i had to risk it ordering online. Either way thank you so so much!