For those of you experienced with using bleach/peroxide - you know how sometimes you only use a little bit for bleaching knots? Well, usually I save the leftovers for usage at another time. So I fold up my bleach powder sachet, and I close the bottle of peroxide and keep it safe.

Then after I few months I bust it out again, mix it up and use it for either highlights or knot bleaching again (there is usually loads left, and I can get a lot out of it). Just wondering if you know how many times this can be done? Does the air react with either the powder bleach or peroxide and render it useless over time?

I'm just asking because in the past I used old bleach/peroxide and my hair looked slightly bleached for 1 or 2 weeks but eventually the effect strangely went away, and my hair darkened again (so I'm assuming the peroxide worked, but the hair didn't get bleached).

Any tips or advice appreciated, because this stuff is €10 a pop and I like to make it go far

Peroxide should be stored in a cool, dark place. Buy small quantities; it loses strength if stored for a long time. Do not use or store peroxide in metal containers, an amber coloured bottle is best and keep it in a cool dark but dry place. If you pour out too much peroxide, do not pour the excess back in the bottle as peroxide is easily contaminated basically the longer you have it once opened the weaker over time it gets Mr. Burns, I hope this helps.